Method and apparatus for measuring electron density of plasma and plasma processing apparatus

ABSTRACT

An apparatus for measuring plasma electron density precisely measures electron density in plasma even under a low electron density condition or high pressure condition. This plasma electron density measuring apparatus includes a vector network analyzer in a measuring unit, which measures a complex reflection coefficient and determines a frequency characteristic of an imaginary part of the coefficient. A resonance frequency at a point where the imaginary part of the complex reflection coefficient is zero-crossed is read and the electron density is calculated based on the resonance frequency by a measurement control unit.

TECHNICAL FIELD

The present invention relates to a technology of monitoring plasma in achamber of a plasma processing apparatus and so on; and moreparticularly, to plasma monitoring method and apparatus for measuringelectron density in plasma and light emission from the plasma.

PRIOR ART

In etching, depositing, oxidizing and sputtering treatments of asemiconductor device or flat panel display (FPD) manufacturing process,plasma is widely used to cause processing gas to desirably react atrelatively low temperatures. Generally, in a plasma processingapparatus, it is necessary to uniformly perform plasma treatment over asurface of a substrate to be processed so as to obtain a high yield. Tothis end, it is necessary to create plasma so that plasma density, i.e.,electron density, is uniformly distributed in a processing space. Fromthis point of view, a technology of precisely measuring electron densityin plasma is indispensable in the design or installation stage of aplasma processing apparatus so as to identify how electron density isdistributed in plasma that is created in the plasma processing space ofa chamber.

Recently, for such a monitoring technology, a plasma absorption probe(PAP) method is attracting attention. This monitoring method uses anantenna probe coated with an insulation pipe, so that it does notdisturb the electrical potential of plasma or does not cause metalliccontamination in a chamber unlike a Langmuir probe method, thus beingcapable of performing measurement in the plasma of reactive gas.Furthermore, the PAP method is advantageous in that the PAP method is ameasurement method in a GHz band, so that the measurement thereof is notaffected by an inductive deposited film even though the inductivedeposited film is attached to the surface of the insulating pipe, andthus, the PAP method can perform measurement even in the plasma ofdeposition gas.

As shown in FIG. 50, in the conventional PAP method (for example, referto Patent Documents 1, 2 and 3), an insulating pipe 202 closed at thefront end thereof is slidably inserted into a through hole 200 aprovided in the sidewall of a chamber 200, a coaxial cable 204 having aprobe portion 204 a formed by exposing several millimeters of the corewire of the front portion of the coaxial cable 204 is inserted into theinsulating pipe 202, and the other end of the coaxial cable 204 isconnected to a scalar network analyzer 206. In the chamber 200, parallelflat plate upper and lower electrodes 208 and 210 connected to, e.g., ahigh frequency power supply (not shown) are arranged as a plasmacreating mechanism, and processing gas is supplied to a gap spacebetween the electrodes 208 and 210 in a depressurized state, thusgenerating the plasma PZ of the processing gas. In the example shown, asubstrate W to be processed is loaded on the lower electrode 210. AnO-ring 212 for supporting the insulating pipe 202 and vacuum-sealing thethrough hole 200 a is fitted into the through hole 200 a provided in thesidewall of the chamber.

The scalar network analyzer 206 transmits a minute power electromagneticsignal (incident wave) to the probe portion 204 a of the coaxial cable204 with respect to each frequency in a band ranging from severalhundred MHz to several GHz while performing frequency sweeping, suchthat the signal is irradiated toward the plasma PZ contained in thechamber 200, and obtains a reflection coefficient in scalar form fromthe ratio of the amount of power of an electromagnetic wave (reflectedwave) reflected from the plasma PZ to the amount of power of theincident wave, thus obtaining the frequency characteristic of thereflection coefficient. In more detail, the probe portion 204 a isplaced at a desired measurement location, the high frequency powersupply for plasma creation is turned off and, simultaneously, the supplyof processing gas is halted, the frequency characteristic of thereflection coefficient Γ(f) (S11 parameter) is obtained by the networkanalyzer 206 in the state where the plasma PZ does not exist in thechamber 200, and the measured data is stored in a memory. Subsequently,by turning on the high frequency power supply and, simultaneously,supplying the processing gas, the frequency characteristic of thereflection coefficient Γ(pf) is obtained by the scalar network analyzer206 in the state where the plasma PZ has been created in the chamber200. Meanwhile, in the frequency characteristics of the ratio of the tworeflection coefficients Γ(pf)/Γ(f), the frequency where a waveform isminimized (has the minimum peak) is considered a plasma absorptionfrequency. Furthermore, this plasma absorption frequency is consideredto be identical with an electron frequency f_(p)(=1/2π√{square root over(e²*N_(e)/m_(e)*ε₀)}) in plasma, so that electron density Ne iscalculated from the following Equation 1.N _(e) =m _(e)*ε₀*(1+ε_(r))*(2πf _(p) /e)²=0.012*(1+ε_(r))*f _(p) ² [m⁻³]  (1)where m_(e) is an electronic mass, ε₀ is a vacuum permittivity, ε_(r) isa relative permittivity of the insulating pipe, and e is an elementaryelectric charge.

To investigate the spatial distribution of electron density in theplasma PZ, the probe portion 204 a is sequentially moved to a pluralityof measurement locations by pushing or pulling the insulating pipe 202in the axial (longitudinal) direction, the frequency characteristics ofreflection coefficients Γ(f) and Γ(pf) are obtained by the scalarnetwork analyzer 206 while the ON and OFF of plasma creation areswitched at each of the measurement locations, and the calculation of aplasma absorption frequency or electron density is performed. Generally,the location of the probe portion 204 a, that is, measurement location,is moved by a desired pitch in steps, and the measured values ofelectron density obtained at respective measurement locations areplotted on a graph.

Furthermore, conventionally, in the development of a plasma processingapparatus, the development of a plasma process, or an actual plasmaprocess, a technology of monitoring plasma light emission in aprocessing chamber has been used. In the conventional plasma lightemission measuring method, plasma light emission in a chamber ismeasured through a window attached to the sidewall of the processingchamber. Typically, spectrum of a certain wavelength is extracted fromplasma light exiting from the processing chamber through the windowusing a spectroscope or an optical filter, and the intensity orvariation of the extracted spectrum is measured (for example, refer toPatent Document 4).

[Patent Document 1]

-   Japanese Unexamined Pat. Publication No. 2000-100598    [Patent Document 2]-   Japanese Unexamined Pat. Publication No. 2000-100599    [Patent Document 3]-   Japanese Unexamined Pat. Publication No. 2001-196199    [Patent Document 4]-   Japanese Unexamined Pat. Publication No. 1998-270417

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, the above-described PAP method is problematic in that themeasured value of a plasma absorption frequency is dependent on awaveform profile in the frequency characteristic of a reflectioncoefficient, so that a deviation easily occurs in the measured value ofelectron density. That is, when an absorption peak (minimum peak)appears as a sharp angled waveform, the frequency of a peak, that is, aplasma absorption frequency, can be precisely measured. However, whenthe absorption peak (minimum peak) appears as a broad waveform having around front end, a peak point is indefinite, so that an error easilyoccurs in a measured value. Such a broad absorption peak waveformappears typically when the plasma density (electron density) of ameasurement point is low. Furthermore, since, under a high pressurecondition, signal power absorption due to collisions between gasmolecules in plasma cannot be ignored, noise is increased, so that it isdifficult to observe the net power absorption based on electronicoscillations, thus reducing S/N.

Furthermore, in the above-described conventional PAP method, since theON and OFF of plasma creation are switched whenever a measurementlocation is changed, a measurement time of several minutes is requiredfor a single measurement location. Furthermore, since the PAT methodslides the insulating pipe 202 to change the measurement location, aconsiderable time is required to move and position the probe portion 202a to and at the next measurement location. For this reason, even whenten measurement points are selected, the total measurement time is atleast several ten minutes. When the spatial distribution of electrondensity is to be precisely evaluated by shortening the step distances orintervals between measurement points, a plurality of measurement points(for example, 100 or more) are necessary, so that the total measurementtime may exceed several hours. Further, when the dependency orcorrelation of electron density on or with the input parameters ofplasma processing (RF power, pressure, gas species, the distance betweenelectrodes, the structure of electrodes, the structure and material of achamber) is to be precisely evaluated, a considerably much measurementtime is required. The problem is more critical, particularly in 300mm-diameter wafer and FPD processing apparatuses having large diameterchambers.

Furthermore, in accordance with the conventional plasma light emissionmeasuring method, plasma light emission in a chamber should be measuredthrough the window of the sidewall of the chamber in the form of anaverage value, but not in the form of a spatial distribution in thechamber. Accordingly, the correlation between the intra-surfacedistribution of the processing results related to a processed substrateand the spatial distribution of plasma light emission cannot beinvestigated.

The present invention has been made keeping in mind the above problemsoccurring in the prior art, and an object of the present invention is toprovide a method and an apparatus for monitoring plasma and a plasmaprocessing apparatus, which are capable of measuring electron density inplasma in high precision in any plasma condition, especially even in alow electron density or high pressure condition.

Another object of the present invention is to provide a method and anapparatus for monitoring plasma which are capable of efficientlymeasuring electron density in plasma in a short time.

Still another object of the present invention is to provide a method andan apparatus for monitoring plasma, which improves the stability anddurability of a probe structure by guaranteeing the reproducibility ofmeasurement locations, improves S/N characteristics by stabilizinginfluence on plasma, and is capable of performing the stable and highlyprecise measurement of electron density in plasma.

Still another object of the present invention is to provide a method andan apparatus for monitoring plasma, which is capable of assuring safetyfor a human body or measurement equipment by effectively preventing theleakage of radio frequency noise to the atmosphere or the measurementequipment.

Still another object of the present invention is to provide a method andan apparatus for monitoring plasma, which has high reliability bymeasuring the light emission of plasma using a spatial distribution in achamber without disturbing the plasma.

Still another object of the present invention is to provide a method andan apparatus for monitoring plasma, which is capable of measuring thelight emission of plasma using a spatial distribution in a chamber evenduring an actual process.

Still another object of the present invention is to provide a plasmaprocessing apparatus, which is capable of assuring the uniformity ofplasma density and further the uniformity of plasma processing for asurface of a substrate to be processed.

To achieve the above-described objects, a method of monitoring plasma inaccordance with a first aspect of the present invention includes thesteps of: placing an antenna probe at a desired monitoring location setinside or near plasma existing within a certain space; causing theantenna probe to irradiate a frequency-variable electromagnetic waveinto the plasma; receiving the electromagnetic wave reflected from theplasma to the probe antenna; measuring a complex reflection coefficientfrom the incident and reflected electromagnetic waves, and obtaining theimaginary part of the complex reflection coefficient; measuring aresonance frequency at which the imaginary part of the complexreflection coefficient is zero by sweeping the frequencies of theelectromagnetic waves; and calculating electron density in the plasmabased on the measured value of the resonance frequency.

Additionally, an apparatus for monitoring plasma in accordance with thefirst aspect of the present invention includes: an antenna probe locatedin the wall of or inside a chamber in or into which plasma is created orintroduced; a vector reflection coefficient measuring unit fortransmitting electromagnetic waves of respective frequencies to theantenna probe while sweeping frequencies to be irradiated to the plasma,receiving reflected waves from the plasma through the antenna probe, andmeasuring complex reflection coefficients; a resonance frequencymeasuring unit for measuring a resonance frequency at which an imaginarypart of the complex reflection coefficients is zero; and an electrondensity operation unit for calculating electron density in the plasmabased on the measured value of the resonance frequency.

In the present invention, a complex reflection coefficient is measuredusing the vector reflection coefficient measuring unit, and an imaginarypart of the complex reflection coefficient is obtained. Furthermore, aresonance frequency at which the imaginary part of the complexreflection coefficient is zero is measured by a resonance frequencymeasuring unit, and the electron density is calculated in plasma by theelectron density operation unit based on the measured value of theresonance frequency. In the present invention, the signal transmissioncharacteristic of plasma reactance with respect to an electromagneticwave is monitored through the imaginary part of the complex reflectioncoefficient, the frequency at which the imaginary part of the complexreflection coefficient is zero is considered a resonance frequency atwhich Landau damping occurs due to the series resonance of the plasmareactance, and the measured electron density is obtained from themeasured value of the resonance frequency.

In accordance with a preferred embodiment of the present invention, thefrequency character of the imaginary part of the complex reflectioncoefficient is obtained by sweeping the frequencies of anelectromagnetic wave by the vector reflection coefficient measuringunit, and a frequency of a point where a sign of the imaginary part ofthe complex reflection coefficient changes from negative (+) to positive(−) or from positive (+) to negative (−) is calculated as the resonancefrequency by a resonance frequency measuring unit based on the frequencycharacteristic.

Furthermore, in accordance with another preferred embodiment of thepresent invention, a first frequency characteristic is obtained withrespect to the imaginary part of the complex reflection coefficient bysweeping the frequencies of the electromagnetic wave in a state wherethe plasma does not exist in the space, a second frequencycharacteristic is obtained with respect to the imaginary part of thecomplex reflection coefficient by sweeping the frequencies of theelectromagnetic wave in a state where the plasma exists in the space,and a normalized frequency characteristic is obtained based on the firstand second frequency characteristics. In accordance with this method,the switching of plasma ON/OFF is performed only once regardless of thenumber of measurement points, so that the total measurement time can beconsiderably reduced.

A plasma processing apparatus in accordance with the present inventionincludes: a chamber for accommodating an object to be processed; a gassupply unit for supplying certain gas into the chamber; a plasmacreation unit for creating plasma, which is used to perform a certaintreatment on the object to be processed, by discharging electricity inthe gas; an exhaust unit for maintaining the chamber at a certainpressure by depressurizing the inside of the chamber; and the plasmamonitoring apparatus of the present invention.

By employing the plasma monitoring apparatus of the present inventionhaving the above-described configuration, the state of plasma density inthe chamber and the status of plasma processing can be preciselymonitored, so that the quality of plasma processing can be improved.

In the plasma processing apparatus of the present invention, a monitorunit for monitoring the state of plasma processing in the chamber basedon the measured value of the electron density obtained from the plasmamonitoring apparatus is provided. More preferably, a process controlunit for controlling at least one of process parameters influencingplasma processing so that the measured value of the electron densityobtained from the plasma monitoring apparatus is maintained within acertain range may be provided.

Additionally, in a preferred embodiment, there is provided a seasoningcontrol unit for performing seasoning based on the characteristic of thetime variation of the measured values of the electron density obtainedfrom the plasma monitoring apparatus with respect to processingconditions after a cleaning of the chamber or a replacement of parts. Ina preferred embodiment, the seasoning control unit obtains arepresentative of the measured values of the electron densitytime-varying during the plasma processing with respect to respectivedummy substrates being processed, completing the seasoning when therepresentative is stabilized to an actual normal value betweensuccessive dummy substrates, and changes a substrate being put into thechamber from the dummy substrate to a normal substrate to be processed.

Additionally, in a preferred embodiment, the antenna probe of the plasmaprocessing apparatus may be attached to the wall of the chamber,electrodes for creating plasma, or a mounting table for supporting anobject to be processed.

Additionally, in a preferred embodiment, a selection switch may beprovided for selecting any one of a plurality of antenna probes arrangedat different locations to be electrically connected to the reflectioncoefficient measuring unit. By electrically connecting the plurality ofantenna probes to the reflection coefficient measuring unit sequentiallyin a time division manner using the selection switch, simultaneousmeasurements at a plurality of monitoring locations can be efficientlyrealized by a single measurement device.

A method of monitoring plasma in accordance with a second aspect of thepresent invention includes the steps of: placing an antenna probe at adesired location set inside or in the vicinity of plasma existing withina certain space; irradiating frequency-variable electromagnetic wavesfrom the antenna probe to the plasma; receiving electromagnetic wavesreflected from the plasma to the antenna probe; measuring a phasedifference between the incident and reflected waves; measuring aresonance frequency at which the phase difference is zero while sweepingthe frequencies of the electromagnetic waves; and calculating electrondensity in the plasma based on the measured value of the resonancefrequency.

Additionally, an apparatus for monitoring plasma in accordance with thesecond aspect of the present invention includes: an antenna probelocated in the wall of or inside a chamber in or into which plasma iscreated or introduced; a phase difference measuring unit fortransmitting electromagnetic waves of respective frequencies to theantenna probe while sweeping frequencies such that the electromagneticwaves are irradiated to the plasma, receiving reflected waves from theplasma through the antenna probe, and measuring a phase differencebetween the incident and reflected waves; a resonance frequencymeasuring unit for obtaining the measured resonance frequency at whichthe phase difference obtained from the phase difference measuring unitis zero, and an electron density operation unit for calculating electrondensity in the plasma based on the measured resonance frequency.

In the method and apparatus for monitoring plasma in accordance with thesecond aspect of the present invention, a sign of in the phasedifference between incident and reflected waves measured by the phasedifference measuring unit corresponds to a sign of the imaginary part ofcomplex reflection coefficient, and the frequency at which a phasedifference is zero is a frequency at which the imaginary part of thecomplex reflection coefficient is zero, that is, a resonance frequency.Accordingly, the highly precise measured value of electron density canbe obtained based on the resonance frequency calculated from the phasedifference.

A method of monitoring plasma in accordance with a third aspect of thepresent invention includes the steps of: inserting and attaching aninsulating pipe into and to a chamber in or into which plasma is createdor introduced; inserting a coaxial cable, which has a probe portionformed by exposing a front core wire of the coaxial cable, into theinsulating pipe; in the state where the plasma does not exist in thechamber, obtaining a first frequency characteristic with respect to areflection coefficient of an electromagnetic wave irradiated from theprobe portion placed in the insulating pipe; in the state where theplasma exists in the chamber, obtaining a second frequencycharacteristic with respect to the reflection coefficient of theelectromagnetic wave irradiated from the probe portion placed in theinsulating pipe; and measuring a plasma absorption frequency based onthe first and second frequency characteristics.

An apparatus for monitoring plasma in accordance with the third aspectof the present invention includes: an insulating pipe inserted andattached into and to a chamber in or into which plasma is created orintroduced; a coaxial cable provided with a probe portion formed byexposing a core wire of a front end of the coaxial cable, and insertedinto the insulating pipe from one end of the insulating pipe; anactuator for moving the coaxial cable in an axial direction of theinsulating pipe; a scalar reflection coefficient measuring unit fortransmitting electromagnetic signals of respective frequencies to theprobe portion of the coaxial cable at certain power while sweepingfrequencies such that the electromagnetic signals are irradiated to asurrounding space, measuring reflection coefficients from the levels ofsignals reflected through the probe portion with respect to therespective frequencies, and obtaining the frequency characteristics ofthe reflection coefficients; and a measurement operation unit forobtaining the measured values of plasma absorption frequencies fromfirst frequency characteristics obtained from the reflection coefficientmeasuring unit in the state where plasma does not exist in the chamberand second frequency characteristics obtained from the reflectioncoefficient measuring unit in the state where plasma exists in thechamber, at measurement locations determined by the locations of theprobe portion.

In the method and apparatus for monitoring plasma in accordance with thethird aspect of the present invention, the measurement of reflectioncoefficients in the state where plasma does not exist in the chamber(OFF state) and the measurement of reflection coefficients in the statewhere plasma exists or is being created in the chamber (ON state) areperformed in batch, respectively, so that the switching of plasma ON/OFFis performed once regardless of the number of measurement points, sothat the total measurement time can be considerably reduced.

In a preferred embodiment of the third aspect, in the state where theplasma does not exist in the chamber, the coaxial cable is moved in anaxial direction of the insulating pipe, and the first frequencycharacteristics are measured at a plurality of measurement locations; inthe state where the plasma exists in the chamber, the coaxial cable ismoved in an axial direction of the insulating pipe, and the secondfrequency characteristics are measured at a plurality of measurementlocations; and a measured value of the plasma absorption frequency isobtained based on the first and second frequency characteristics at theplurality of measurement locations. In this case, preferably, the probeportion is sequentially positioned at the plurality of measurementlocations, and the first and second frequency characteristics may beobtained at the plurality of measurement locations with respect to thereflection coefficients of the electromagnetic wave irradiated from theprobe portion. In this embodiment, the probe portion is sequentiallypositioned at respective measurement locations at short tact intervalsin a plasma OFF or ON state, and a measured data of reflectioncoefficients can be obtained at all the measurement locations in a shorttime. Preferably, the probe portion may be sequentially positioned atthe plurality of measurement locations by pulling the coaxial cable outof the insulating pipe, through the use of an actuator.

In a preferred embodiment of the present invention, the insulating pipeaccommodating a coaxial cable equipped with a probe portion is hungbetween first and second supports provided in the sidewalls of thechamber. In this case, at least one of the first and second supports maybe formed of a through hole. Furthermore, the insulating pipe may beairtightly and fixedly attached in the through hole using an O-ring.

In accordance with such bridge-type insulating pipe mounting structure,the insulating pipe is supported at two locations (first and secondsupports) on the wall of the chamber, so tat the insulating pipe is notvibrated by an operation of positioning the probe and is not bent by itsown weight. Accordingly, the probe portion can be rapidly and preciselypositioned at a desired measurement location and can be located at apoint on a line, so that the reproducibility of measurement locationscan be guaranteed. Furthermore, at the time of positioning the probe,the coaxial cable is preferably moved in an axial direction of theinsulating pipe fixed to the chamber. Since there is no friction betweenthe insulating pipe and the support, there is no concern for the damageor deterioration of the support. Accordingly, the stability of a probemechanism is proved, so that the cost of consumables is reduced.Furthermore, the disturbance of plasma attributable to the probemechanism is uniform regardless of measurement locations, so that thereliability of the measurement is high. The insulating pipe has acoaxial pipe structure that is constant or uniform at any measurementlocation when viewed from the probe portion of the coaxial cable, andthe coupling of an electromagnetic wave generated from the probe portionwith plasma is constant, so that an generation of noise is suppressed,so that measurement having high precision and reproducibility can beguaranteed. Further, an insulating pipe mounting structure in which theinsulating pipe is attached in the chamber by a single support, e.g., acantilever is also possible.

In the present invention, the outer conductor of the coaxial cable maybe electrically connected to a grounding potential through the chamber.In particular, there may be provided a grounding conductor one end ofwhich is connected to a grounding potential portion of the chamber andthe other end of which is connected to the outer conductor of thecoaxial cable. In accordance with this method or configuration, theleakage of RF noise to the atmosphere or the measuring unit iseffectively prevented, so that the safety of the human body or ameasurement device is guaranteed while avoiding the malfunction ofsurrounding electronic equipment, such as a gas detector.

Preferably, a noise signal (typically, a noise signal attributable to astanding wave propagating along the outer conductor) may be absorbedinto an electromagnetic wave absorber through electromagnetic inductionat a location around the probe portion side of the coaxial cable whenviewed from the location where the grounding conductor and the outerconductor of the coaxial cable are in contact with each other. Theelectromagnetic wave absorber preferably is one or more bead-shapedferrite members placed around the coaxial cable along the axialdirection thereof. In accordance with this method or configuration, eventhough noise, such as standing wave noise, occurs on the outer conductor(grounding portion), the noise can be effectively absorbed andeliminated by the electromagnetic wave absorber.

Preferably, cooling gas may be allowed to flow in the insulating pipethrough an opening formed at the other end of the insulating pipe. Inparticular, the other end of the insulating pipe is opened, and acooling device for allowing the cooling gas to flow may be connected tothe opening. In accordance with this method or configuration, thecoaxial cable in the insulating pipe can be effectively cooled, so thatthermal expansion or thermal damage around the probe portion can beprevented, thus improving its durability.

A method of monitoring plasma in accordance with a fourth aspect of thepresent invention includes the steps of: inserting and attaching atransparent insulating pipe into and to a chamber in or into whichplasma is created or introduced; inserting a rod-shaped opticaltransmission probe, which has a light receiving surface at a front endthereof, into the insulating pipe from one end of the insulating pipe;and allowing light generated by the plasma in the chamber to be incidenton the light receiving surface of the probe through the insulating pipe,and measuring light emission from the plasma based on light irradiatedfrom the other end of the probe.

An apparatus for monitoring plasma in accordance with the fourth aspectof the present invention includes: a transparent insulating pipeinserted and attached into and to a chamber in or into which plasma iscreated or introduced; a rod-shaped light transmission probe providedwith a light receiving surface at a front end thereof, and inserted intothe insulating pipe from one end of the insulating pipe; and ameasurement unit for measuring light emission from the plasma based onlight irradiated from the other end of the probe.

In the plasma light emission monitoring method of the present invention,the insulating pipe is inserted into the chamber, the rod-shaped opticaltransmission probe is moved in the insulating pipe in an axial directionthereof, light emission from plasma is collected on the light receivingsurface of the probe at a measurement location in the axial direction,the collected plasma light is transmitted to the measurement unit, and ameasured value of a certain characteristic or attribute (for example, acertain wavelength or the intensity of a spectrum) is obtained by themeasurement unit with respect to plasma emission at each measurementlocation. In this case, the insulating pipe and the probe are made ofnon-metal, which does not disturb the plasma even though being insertedinto the plasma in the chamber, thereby performing highly reliable andprecise spatial distribution measurement.

In a preferred embodiment of the present invention, the probe is movedin the insulating pipe in the axial direction thereof (preferably, in aradial direction of the chamber), and the plasma light emission ismeasured in the form of a spatial distribution along the axialdirection. In this case, the axial direction of the probe may coincidewith the radial direction of the chamber. Alternately, the probe,together with the insulating pipe, is moved in a height direction, andthe plasma light is measured in the form of a spatial distribution inthe height direction.

In the present invention, the probe may be made of quartz or sapphire.However, to block faint light emitting from the side thereof, the probepreferably has a dual structure that includes a core made of quartz orsapphire and a cladding placed around the core. The probe preferably hasa light shielding coating thereon. Furthermore, the probe is preferablyconstructed to include a bundle of optical fibers and a heat-resistantnon-metallic member, such as polyamide, surrounding the optical fibers.

To improve the light collecting function of the probe, in particular,its directionality, plasma light incident from a desired direction ispreferably guided to be incident on a mirror at the front end of theprobe such that the plasma light reflected by the mirror is incident onthe light receiving surface of the probe. More preferably, a lightshielding member is attached to the front end of the probe to surroundthe light receiving surface and the mirror, and the plasma lightincident from a desired direction is made to be incident on the mirrorthrough a window provided on the light shielding member. A reflectingsurface of the mirror is preferably made of aluminum having a certainhigh reflection factor with respect to rays ranging from an ultravioletray to an infrared ray.

To allow undesired light to be incident on the bundle fiber at an anglelarger than the numerical aperture of the bundle fiber, one end of theprobe is preferably cut so that the normal line of the light receivingsurface of the probe is inclined toward the window at a certain anglewith respect to the axial direction of the probe.

In the present invention, the material of the transparent insulatingpipe preferably is quartz or sapphire having superior wavelengthtransmittance, heat-resistant property and anti-corrosion property. Toperform the stable and high speed scanning of the probe, the insulatingpipe is preferably hung between first and second supports provided to beopposed to each other in the sidewalls of the chamber.

In a method of monitoring plasma in accordance with a fifth aspect ofthe present invention, an opening, which is selectively opened andclosed, is provided in the sidewall of a chamber in or into which plasmais created or introduced, a rod-shaped optical transmission probe, whichhas a light receiving surface at a front end thereof, is inserted intothe chamber from the opening in a depressurized space, and lightemission from the plasma is measured based on light irradiated from theother end of the probe.

Further, a plasma light emission measuring apparatus in accordance withthe fifth aspect of the present invention includes: an opening, which isselectively opened and closed, provided in the sidewall of a chamber inor into which plasma is created or introduced; a rod-shaped opticaltransmission probe provided with a light receiving surface at a frontend thereof, and inserted into the chamber from the opening in adepressurized space; and a measurement unit for measuring light emissionfrom the plasma based on light irradiated from the other end of theprobe.

In this scheme, the probe is inserted into the chamber from the openingof the sidewall of the chamber while the opening is opened, the probe ismoved in the axial direction thereof (preferably, in the radialdirection of the chamber), the plasma light collected on the lightreceiving surface of the probe is transmitted to the measurement unit,and a measured value of a certain characteristic or attribute (forexample, a certain wavelength or the intensity of a spectrum) isobtained with respect to plasma light emission at each measurementlocation using the measurement unit. Preferably, the variation of plasmalight is obtained with respect to the moving distance of the probe, andthe plasma light may be measured in the form of a spatial distributionin the chamber in the axial direction of the probe. The probe preferablyincludes a core made of quartz or sapphire and a cladding placed aroundthe core.

Further, in order to form a depressurized space around the probe outsidethe chamber, an expansible and contractible bellows is preferablyprovided in the radial direction of the chamber and the inner space ofthe bellows may be exhausted of air through an exhaust unit.Furthermore, to prevent a reaction product (deposit) from adhering tothe probe when the probe is exposed to a plasma region in the chamber,it is preferable to heat the probe to an appropriate temperature outsidethe chamber.

In this scheme, the plasma is not disturbed by the probe because theprobe is made of non-metal, and processing results are not influencedbecause probe scanning can be performed in a short time at high speed,so that the scheme can be applied to the development of a process aswell as an actual process.

In the plasma light emission monitoring method, the actuator ispreferably used to move the probe in the axial direction, and stable andhigh-speed probe scanning can be performed by the forward operation ofthe actuator. Further, in the measuring processing of the presentinvention, a certain wavelength spectrum is extracted from lightirradiated from the outer end of the probe by a spectroscope(spectroscope or optical filter), and the intensity of the correspondingspectrum may be measured. Further, the light irradiated from the otherend of the probe is preferably provided to the measurement unit throughthe bundle fiber. In this way, the light emission of the plasma can bemeasured with directionality equal or equivalent to that of the casewhere the light receiving surface of the bundle fiber is put into thechamber.

Effects of the Invention

In accordance with the present invention, electron density in plasma canbe accurately and precisely measured by employing the above-describedconfiguration and operation under arbitrary plasma conditions, inparticular, a low electron density condition or high pressure condition.Further, the uniformity of plasma density or the quality of plasmaprocessing can be improved based on the highly reliable measured valuesof electron density. Furthermore, it is possible to efficiently measurea plasma resonance frequency or electron density in a short time.Furthermore, the stability and durability of a probe structure areimproved by guaranteeing the reproducibility of measurement locations,S/N characteristics are improved by stabilizing or eliminating aninfluence of the probe on plasma, and thus the stable and highly precisemeasurement of a plasma resonance frequency or electron density can beperformed. Plasma light emission can be measured with high reliabilityand precision in the form of a spatial distribution within a chamberwithout disturbing the plasma. Furthermore, the uniformity of plasmadensity and further the uniformity of plasma processing on a surface ofa substrate to be processed are guaranteed, so that a yield can beimproved.

Best Modes for Carrying out the Invention

In the following, with reference to FIGS. 1 to 49, preferred embodimentsof the present invention will be described in detail.

EMBODIMENT 1

With reference to FIGS. 1 to 18, a first embodiment of the presentinvention is described. FIGS. 1 and 2 show a configuration of a plasmaprocessing apparatus, to which a method and an apparatus for measuringelectron density of plasma are applied, in accordance with a firstembodiment of the present invention. This plasma processing apparatus isa capacitively coupled parallel flat plate type plasma processingapparatus.

A chamber 10 of the plasma processing apparatus is made of, for example,aluminum, and is composed of a processing chamber that is cylindricallyshaped and can be sealed. A support 14 made of, e.g., aluminum is placedon the bottom of the chamber 10 with an insulating plate 12 beinginterposed therebetween, and a susceptor 16 made of, e.g., aluminum isseated on the support 14. The susceptor 16 constitutes a lowerelectrode, and a substrate to be processed, such as a semiconductorwafer W, is mounted thereon.

A high frequency power supply 18 for supplying high-frequency power toattract ions is electrically connected to the susceptor 16 through amatching unit (not shown), and additionally, a High-Pass Filter (HPF) 22for passing therethrough a high frequency wave applied from an upperelectrode to be described below is electrically connected to thesusceptor 16. An electrostatic chuck (not shown) for securing andmaintaining the substrate W using, e.g., electrostatic attraction may beplaced on the upper surface of the susceptor 16. Furthermore, a coolingor heating means (not shown) for controlling temperature may be providedin the susceptor 16 or support 14.

An upper electrode 24 is located above the susceptor 16 to face thesusceptor 16 in parallel. The upper electrode 24 is supported in thechamber 10 through via a cylindrical insulating member 25. The upperelectrode 24 has a lower electrode plate 28 provided with a plurality ofgas discharge holes 26 and made of, for example, a ceramic, such as analumina, and an electrode support 30 made of a conductive material, suchas an aluminum surface-treated with an alumite. A buffer chamber isformed inside the electrode plate 28 and the electrode support 30, and agas introduction hole 32 is formed at the upper side of the bufferchamber. Gas supply piping 36 extending from a processing gas supplysource 34 is connected to the gas introducing hole 32. A high frequencypower supply 38 for supplying high-frequency power to generate plasma iselectrically connected to the upper electrode 24 through a matching unit(not shown), and additionally, a Low-Pass Filter (LPF) 42 for passing ahigh frequency wave applied from the susceptor (lower electrode) 16 iselectrically connected to the upper electrode 24.

An exhaust hole 44 is formed in the bottom of the chamber 10, and anexhaust unit 46 is connected to the exhaust hole 44 through an exhaustpipe. This exhaust unit 46 has a vacuum pump such as a turbo molecularpump, and is capable of depressurize a processing space within thechamber 10 to a certain vacuum level. Further, an opening and closingmechanism, e.g., a substrate entrance equipped with a gate valve, isformed in the sidewall of the chamber 10 to allow the substrate W to beput and drawn into and from the chamber 10. The chamber 10 is groundedthrough an earth wire.

In the plasma processing apparatus, when the substrate W placed on thesusceptor 16 is plasma-processed, under the control of a main controlunit 20, a predetermined amount of required processing gas is introducedfrom the processing gas supply unit 34 to the chamber 10 and thepressure of the chamber 10 is adjusted to a set value using the exhaustunit 46. Further, high frequency power at a predetermined frequency (forexample, 2 MHz) supplied from the high frequency power supply 18 andhigh frequency power at a predetermined frequency (for example, 60 MHz)supplied from the high frequency power supply 38 are applied to thesusceptor (lower electrode) 16 and the upper electrode 24, respectively.The processing gas discharged from the porous electrode plate or showerhead 28 of the upper electrode 24 is converted into plasma during a glowdischarge between the electrodes, and the substrate W is plasmaprocessed by radicals or ions contained in the plasma PZ. Furthermore,the distance between the susceptor (lower electrode) 16 and the upperelectrode 24 is set to, for example, 10 to 60 mm.

In the present embodiment, a plasma electron density measuring apparatusincludes: a cylindrical insulating pipe 50 fixedly attached to thechamber 10; a coaxial cable 52 provided with a probe portion (antennaprobe) 52 a formed by exposing a core wire of a front end of the coaxialcable 52, and slidabley inserted into one end (left-hand end in FIG. 1)of the insulating pipe 50; a measuring unit 54 for measuring a resonancefrequency and electron density through the coaxial cable 52 with respectto the plasma PZ generated in the chamber 10; and a linear actuator 56for moving the coaxial cable 52 in an axial direction thereof.

The insulating pipe 50 is formed of, for example, a quartz pipe having astraight-line shape, is slightly longer than the outer diameter of thechamber 10, and is open at both ends thereof. As shown in FIG. 1, twothrough holes 10 a facing to each other are formed in the sidewalls ofthe chamber 10 at center positions between the susceptor (lowerelectrode) 16 and the upper electrode 24 to be used as supports ormeasurement ports, and the insulating pipe 50 passes through the throughholes 10 a and are horizontally positioned across the chamber 10.O-rings 58 are fitted into the through holes 10 a to hold the insulatingpipe 50 in an airtight manner, that is, a vacuum sealing manner.

The coaxial cable 52, as shown in FIGS. 2A and 2B, is formed of asemi-rigid cable that includes a core wire (inner conductor) 52 a madeof, e.g., aluminum, an outer conductor 52 b made of a stainless pipe,and an insulating member 52 c made of Teflon®. The probe portion isformed by exposing the core wire 52 a of the front end of the coaxialcable 52 by several mm. A base side of the coaxial cable 52 is connectedto the measuring unit 54 in the form of an SMA plug 60 (FIG. 1).Further, the outer conductor (ground portion) 52 b of the coaxial cable52 protruded from the insulating pipe 50 is electrically connected tothe sidewall of the chamber 10 having a ground potential via a groundingconductor 62.

As shown in FIG. 2A, the grounding conductor 62 is, e.g., fixedlymounted on a conductive flange member 64, to which the insulating pipe50 is attached and fixed, at a base thereof, and an front end of theground conductor 62 may be composed of a plurality of conductive springmembers which come into slidable contact with the outer conductor 52 bof the coaxial cable 52. Further, the conductive spring members mayelastically hold the coaxial cable 52 at a certain location therebetweenin a vertical or horizontal direction. Alternately, conductive wiresinstead of the spring members may be used. In this case, the front endsof the conductive wires may be connected to the outer conductor 52 b ofthe coaxial cable 52 by means of clips. In any case, the probe portion52 a is preferably positioned at a desired location (measurementlocation) by inserting the coaxial cable 52 into the insulating pipe 50at the state where the grounding conductor 62 is opened (released) andmoving the coaxial cable 52 in the direction of pulling thereof out ofthe insulating pipe 50.

An electromagnetic wave absorber is provided in the vicinity of andinside the grounding conductor 62, that is, at the location of the probeportion side, to absorb the noise signal of a standing wave generated onthe outer conductor 52 b of the coaxial cable 52. In the presentembodiment, as shown in FIG. 2A, one or more bead-shaped ferrite members66 are attached to a cylindrical insulating retainer 65 in series in theaxial direction of a retainer 65 which the coaxial cable 52 is passedthrough.

As shown in FIG. 1, the measuring unit 54 includes a vector networkanalyzer 68 that is a main body of the measuring unit 54, a RF limiter70 and a HPF 72 used to perform an SMA interface, and a measurementcontrol unit 74 for performing control and operation processes formeasurement. The configuration of the vector network analyzer 68 and themeasurement control unit 74 will be described later in detail.

The linear actuator 56 includes a slider 76 combined with the base ofthe coaxial cable 52, and a ball-screw mechanism 78 configured torectilinearly move the slider 76 in the axial direction of the coaxialcable 52. For example, a servomotor (not shown) may be used as a drivingdevice for the ball-screw mechanism 78, which is adapted to position theslider 76 at a certain location within a moving range of the slider 76.

Piping 82 extending from a cooling gas supply unit 80 is connected tothe other end (a right end of FIG. 1) of the insulating pipe 50. Thecooling gas supply unit 80 has, e.g., a blower or pump so that coolinggas such as air flows into the insulating pipe 50 through the piping 82.The air introduced into the right end of the insulating pipe 50 flowsthrough the insulating pipe 50 toward the left end of the insulatingpipe 50, and is discharged into the atmosphere through the gaps of thegrounding conductor 62. As described above, the air flows through theinsulating pipe 50 in the axial direction thereof, so that thesurrounding of the coaxial cable 52, especially, the probe portion 52 a,can be effectively cooled. More preferably, the cooling gas supply unit80 may supply cooling gas the temperature of which has been adjusted.Alternately, it is possible to construct the cooling gas supply unit 80in an air suction type, so that the air flows in the insulating pipe 50from the left side to the right side thereof.

FIG. 3 illustrates principal parts of the vector network analyzer 68 andthe measurement control unit 74 of the measurement unit 54.

The vector network analyzer 68 includes a reflection coefficientmeasuring unit 84 for performing signal transmission/reception andsignal processing to measure a reflection coefficient in complex numberform (complex reflection coefficient), a buffer memory 86 fortemporarily storing temporary data of measured reflection coefficientvalues (frequency characteristics), and a real part memory 88 and animaginary part memory 90 for storing respectively the real part Γ_(r)and the imaginary part Γ_(I) of a final data (frequency characteristics)Γ of the reflection coefficient measuring unit 84. The reflectioncoefficient measuring unit 84 includes a frequency sweeping type highfrequency power supply, a directional coupler for detecting an incidentwave and a reflected wave and a complex reflection coefficientmeasurement circuit. The complex reflection coefficient measurementcircuit may be implemented by employing, e.g., an amplitude ratiomeasurement circuit and a phase difference measurement circuit.

While a scalar network analyzer obtains a measured value in scalar formfrom the ratio of the power (scalar) of a reflected wave to the power(scalar) of an incident wave, the vector network analyzer 68 of thepresent embodiment measures a reflection coefficient Γ(Γ_(r)+jΓ_(i)) incomplex number form from a ratio V_(re)/V_(in) of voltages V_(re) andV_(in) or a ratio I_(re)/I_(in) of currents I_(re) and I_(in). In thiscase, an imaginary part Γ_(i) takes a positive or negative signdepending on a frequency.

The measurement control unit 74 includes a resonance frequencydetermining unit 92 for receiving the measured value data (frequencycharacteristic) of the imaginary part Γ_(i) of a complex reflectioncoefficient from the imaginary part memory 90 of the vector networkanalyzer 68 and determining a resonance frequency f_(p) by countingzero-crossing points thereof, an electron density operation unit 94 forcalculating an electron density N_(e) using a predetermined calculationequation based on the resonance frequency f_(p) calculated by theresonance frequency determining unit 92, an output unit 96 foroutputting data of the measured electron density N_(e), and a sequencecontrol unit 98 for controlling a sequence of measurements.

Hereinafter, a method of measuring an electron density of the plasma PZin the chamber 10 at a specific location in the radial direction of thechamber 10 in the plasma electron density measurement apparatus of thepresent embodiment is described below.

In the present embodiment, the measurement of a plasma electron densityis performed as described below under the control of the coefficientcontrol unit 74 (in particular, a sequence control unit 98) of themeasuring unit 54. First, the probe portion 52 a is positioned at adesired measurement location h_(k) by moving the coaxial cable 52through the insulating pipe 50 along the axial direction thereof(preferably, in the direction of pulling thereof) using the linearactuator 56.

Next, the vector network analyzer 68 obtains a measured value (frequencycharacteristic) of a complex reflection coefficient Γ at the measurementlocation h_(k) through the RF limiter 70, the HPF 72, the coaxial cable52 and the probe portion 52 a. In this case, for a referencemeasurement, at a first measurement step, the frequency characteristic(first frequency characteristic Γ(f)) of a complex reflectioncoefficient Γ is obtained in a plasma OFF state where the plasma PZ doesnot exist in the chamber 10, as shown in FIG. 4. Thereafter, at a secondmeasurement step, the frequency characteristic (second frequencycharacteristic Γ(pf)) of a complex reflection coefficient Γ is obtainedin a plasma ON state where the plasma PZ exists in the chamber 10, asshown in FIG. 5.

At the first and second measurement steps, the reflection coefficientmeasuring unit 84 of the network analyzer 68 transmits anelectromagnetic signal (incident wave) of, e.g., about 1 mW to the probeportion 52 a of the coaxial cable 52 with respect to each frequencywhile performing frequency sweeping in a band, e.g., ranging fromseveral hundred MHz to several GHz, so that the electromagnetic signalis irradiated to a surrounding space (along a radial direction whenviewed from the probe portion 52 a) and is incident on the surroundingplasma PZ. Thereafter, the electromagnetic wave, i.e., a reflected wave,returned from the plasma PZ to the probe portion 52 a is received, andthe incident wave and the reflected wave are compared with each otherusing the complex reflection coefficient measurement circuit after beingpassed through the directional coupler, thus obtaining a measured valueof the reflection coefficient Γ(Γ_(r)+jΓ_(i)) in complex number form.

Subsequently, a normalized frequency characteristic is obtained from thefirst frequency characteristic Γk(f) obtained at the first step and thesecond frequency characteristic Γk(pf) obtained at the second stepthrough a specific operation, for example, division Γk(pf)/Γk(f). Of themeasured value (frequency characteristic) of the reflection coefficientΓ(Γ_(r)+jΓ_(i)) in complex number form, the real part Γr thereof isstored in the real part memory 88 while the imaginary part Γ_(i) thereofis stored in the imaginary part memory 90. In the present embodiment,the measured value (frequency characteristic) of the complex reflectioncoefficient Γ_(i) stored in the imaginary part memory 90 is effectivelyused.

FIG. 6 shows an example (experimental data) of the frequencycharacteristics of an absolute value |Γ|, the real part Γ_(r) and theimaginary part Γ_(I) of the reflection coefficient Γ(Γ_(r)+jΓ_(i)). Thisexperimental data is obtained at a measurement location R=0 mm (a centerpoint of the chamber) under the plasma cleaning conditions in which thepressure of the chamber 10 is 15 mTorr, lower RF power (2 MHz) suppliedfrom the high frequency power supply 18 is 200 W, upper RF power (60MHz) supplied from the high frequency power supply 38 is 1500 W, andprocessing gas is O₂ (200 sccm). In FIG. 6, the absolute value |Γ| ofthe reflection coefficient Γ corresponds to the reflection coefficientobtained in scalar form by the scalar network analyzer, has a valuealmost identical with the value of the real part Γ_(r), and does notactually reflect the value of the imaginary part Γ_(i).

Referring to the frequency characteristic of the absolute value |Γ| ofthe complex reflection coefficient Γ, it is considered that a minimumpeak of the absolute value |Γ| corresponds to a maximum peak of powerabsorption attributable to electron oscillations, and the frequency atthe time of having the minimum (absorption) peak, that is, plasmaabsorption frequency, corresponds to an electron frequency. However, ifthe minimum peak waveform of the absolute value |Γ| becomes broad or anamount of a noise component increases, it is difficult to preciselycalculate the plasma absorption frequency, so that a measurement erroreasily occurs. In contrast, in the present invention, based on thewaveforms (frequency characteristics) of the imaginary part Γ_(i) of areflection coefficient Γ, a frequency at which Γ_(r) is zero-crossing isassumed to be a plasma resonance frequency. Further, the plasmaresonance frequency is considered to correspond to a electron frequency,thus being converted into electron density, as will be described below.

In the coefficient control unit 74, the resonance frequency determiningunit 92 receives the measured value (frequency characteristic) of theimaginary part Γ_(i) of the complex reflection coefficient from theimaginary part memory 90 of the vector network analyzer 68, anddetermines a frequency of a zero-crossing point. As described above, theimaginary part Γ_(i) of the complex reflection coefficient has apositive or negative sign depending on the frequency. Generally, in thefrequency characteristic of the imaginary part Γ_(i) by frequencysweeping, a zero-crossing point ZC appears at a single point as shown inFIG. 6, Γ_(i) has a negative (minus) value in a frequency domain belowthe zero-cross point ZC, and Γ_(i) has a positive (plus) value in afrequency domain above the zero-cross point ZC. When viewed from thesweeping direction in which the frequency increases, the value of Γ_(i)changes from a minus value to a plus value at the zero-cross point ZC.On the contrary, when viewed from the sweeping direction in which thefrequency decreases, the value of Γ_(i) changes from a plus value to aminus value at the zero-cross point ZC. As described above, thefrequency of the zero-cross point ZC is the frequency of the point atwhich the sign of Γ_(i) is reversed, and can be simply and accuratelycalculated regardless of the waveform profile of frequencycharacteristics. In the present invention, the frequency of thezero-cross point is defined as a resonance frequency f_(p).

Hereinafter, a basic principle of the electron density measuring methodis described. The probe portion 52 a of the coaxial cable 52 iselectrically connected to the plasma PZ in the chamber 10 through theinsulating pipe 50. When the complex impedance Z_(p) of the plasma PZ atthe measurement location h_(k) is set to R+jX and the impedance of theinsulating pipe 50 is ignored, the complex reflection coefficientΓ(Γ_(r)+jΓ_(i)) is expressed as Equation 2 in terms of impedance.

$\begin{matrix}\begin{matrix}{\Gamma = {\left( {\Gamma_{r} + {j\;\Gamma_{i}}} \right) = {\left( {Z_{p} - 50} \right)/\left( {Z_{p} + 50} \right)}}} \\\left. {= {{\left\{ {\left( {R + {jX}} \right) - 50} \right\}/\left\{ {R + {jX}} \right\}} + 50}} \right\} \\{= {\left\{ {\left( {R - 50} \right) + {jX}} \right\}/\left\{ {\left( {R + 50} \right) + {jX}} \right\}}}\end{matrix} & {{Eq}.\mspace{14mu}(2)}\end{matrix}$

The constant “50 (Ω)” of the right side of Equation 2 is thecharacteristic impedance of the coaxial cable 52. By rationalizeEquation 2, Equation 3 can be obtained.Γ(Γ_(r) +jΓ _(i))=(AB+X ²)/(B ² +X ²)+j100X/(B ² +X ²)  Eq. (3)where A=R−50 and B=R+50.

When viewed from the probe portion 52 a, the plasma PZ is composed of anion sheath of a capacitive load that is formed along the surface of theinsulating pipe 50 and bulk plasma of an inductive load. The ion sheathhas capacitive reactance X_(C) and the bulk plasma has inductivereactance X_(L). Both of them form a series circuit between the probeportion 52 a and a reference potential (ground potential). When thecapacitive reactance X_(C) of the sheath is higher than the inductivereactance X_(L) of the bulk plasma, resultant reactance X is minus, andcorrespondingly, the value of the imaginary part Γ_(i) of the complexreflection coefficient is minus. When the inductive reactance X_(L) ofthe bulk plasma is higher than the capacitive reactance X_(C) of thesheath, resultant reactance X is plus, and correspondingly, the value ofthe imaginary part Γ_(i) of the complex reflection coefficient is plus.When the capacitive reactance X_(C) of the sheath is equal to theinductive reactance X_(L) of the bulk plasma, resultant reactance X iszero, and therefore, series resonance is formed. In this case, theimaginary part Γ_(i) becomes zero. In a series resonant state, signalpower transmission attributable to the plasma reactance X is maximizedand the energy of an incident wave from the probe portion 52 a istransmitted to electrons in the plasma through a so-called Landaudamping mechanism. That is, when a series resonance state isestablished, the frequency of the electromagnetic wave, i.e., theresonance frequency, coincides with or is matched with the electronfrequency. In the present invention, in the frequency characteristic ofthe imaginary part Γ_(i) of the complex reflection coefficient, thefrequency at the zero-cross point is considered to be the frequencyf_(p) at which the sheath capacitance and bulk inductance of the plasmaresonate in series, and a measured value of the electron density isobtained from a measured value of the resonance frequency f_(p). Inpractice, the normalization of the reflection coefficient Γk(pf)/Γk(f)is performed by the vector network analyzer 68 as described above, sothat Equation 3 is modified, but basically, the above-described theoryis adequate.

In the coefficient control unit 74, the measured value of the resonancefrequency f_(p) obtained from the resonance frequency determining unit92 is applied to the electron density operation unit 94. Since theresonance frequency f_(p) propagates through the insulating pipe 50having a relative permittivity of ε_(r) at a frequency of √{square rootover ((1+ε_(r))*f_(p))}, as described above, it can be considered that√{square root over ((1+ε_(r))*f_(p))} is identical with electronfrequency 1/2π*√{square root over (e²*N_(e)/m_(e)*ε₀)} in plasma. Theelectron density operation unit 94 can calculate electron density N_(e)using Equation 4.

$\begin{matrix}\begin{matrix}{N_{e} = {m_{e}*ɛ_{0}*\left( {1 + ɛ_{r}} \right)*\left( {2\pi\;{f_{p}/e}} \right)^{2}}} \\{= {5.96\mspace{11mu}{E10}\mspace{11mu}{\left( f_{p} \right)^{2}\mspace{14mu}\left\lbrack {cm}^{- 3} \right\rbrack}}}\end{matrix} & {{Eq}.\mspace{14mu}(4)}\end{matrix}$where m_(e) is electron mass, ε₀ is vacuum, permittivity, ε_(r) is arelative permittivity of the insulating pipe (about 3.8) and e iselementary electric charge. Furthermore, a unit of f_(p) is GHz, and E10designates 10¹⁰.

FIGS. 7A and 7B show an example (experimental data) of the measurementsensitivity of electron density obtained by the plasma resonance probemethod of the present invention. This experimental data shows the timevariations of electron density N_(e) immediately after the initiation ofplasma ON at measurement locations of R=80 mm (80 mm away from thecenter point of the chamber in the radial direction of the chamber; FIG.7A) and R=220 mm (220 mm away from the center point of the chamber inthe radial direction of the chamber, 20 mm away from the sidewall of thechamber; FIG. 7B) under the plasma cleaning conditions in which thepressure of the chamber 10 is 15 mTorr, lower RF power (2 MHz) is 200 W,processing gas is O₂ (200 sccm) and upper RF power (60 MHz) is minutelyvaried around 1500 W.

As shown in the drawings, when the upper RF power is varied from thecentral value 1500 W by ±30 W (2%), at the measurement location of R=80mm (FIG. 7A), it is read that the electron density N_(e) is varied byabout ±0.1E+10 (E+10=10¹⁰). Meanwhile, at the measurement location ofR=220 mm (FIG. 7B), it is read that the electron density N_(e) is variedby about ±0.02E+10. In general, in the case where RF power forgenerating plasma is a process parameter, if the variation of electrondensity is monitored when the RF power is varied by 2%, it is sufficientin terms of specifications, and the plasma electron density measurementmethod of the present invention can desirably meet the requirement. Itis a noteworthy that the electron density N_(e) can be measured in highprecision even at the measurement location near the sidewall of thechamber where plasma density is low.

In FIG. 8, to compare measurement precisions, the measurement values ofelectron density N_(e) obtained by the plasma resonance probe method ofthe present invention at a measurement location of R=80 mm is comparedwith those obtained by the plasma absorption probe (PAP) method at thesame location. Process conditions are the same as those of theexperiments shown in FIGS. 7A and 7B (however, upper RF power is 1500W). As apparent from FIG. 8, while the variations (waveform) of electrondensity obtained by the PAP method show large fluctuations inmeasurement values, the variations (waveform) of electron densityobtained by the present invention show small differences in measurementvalues, and therefore, appear in the form of a smooth curve.

Another advantage of the present invention is the fact that the electrondensity in the plasma can be accurately measured under a high pressurecondition. FIGS. 9, 10 and 11 show the frequency characteristics(experimental data) of complex reflection coefficients when thepressures of the chamber are 15 mTorr, 800 mTorr and 1600 mTorr,respectively. In the drawings, Γ_(i) is the imaginary part of thecomplex reflection coefficient Γ obtained by employing the presentinvention, and the |Γ| is the absolute value of the complex reflectioncoefficient and corresponds to the reflection coefficient in scalarform, which is obtained by the PAP method. In this experiment, there wasused a micro-waveform plasma procession apparatus for plasma chemicalvapor deposition (CVD), which created plasma by irradiating microwavesof a high frequency (2.45 GHz) produced by a magnetron, from the quartzwindow of the ceiling of the chamber through a wave guide into thechamber. The experiment was carried out under process conditions inwhich gas is Ar (400 sccm) and power of microwaves is 1000 W.

Referring to the frequency characteristics of the absolute value |Γ| ofthe complex reflection coefficient corresponding to the frequencycharacteristics of the reflection coefficient based on the PAP method,under the condition of a pressure of 15 mTorr (FIG. 9), the minimum(absorption) peak exhibits a shape-angled waveform and a frequency(absorption frequency) corresponding to the peak point can be accuratelyread. However, under the condition of a pressure of 800 mTorr (FIG. 10),the minimum (absorption) peak waveform is rounded and broadened, a peakpoint is indefinite and the number of noise components, which may beconfused with the minimum peak waveform, increases. Meanwhile, under thecondition of a pressure of 1600 mTorr (FIG. 11), this tendency isremarkable and it is difficult to accurately calculate an absorptionfrequency. The reason for this is that when pressure increases, thenumber of collisions between electrons and particles in the plasma (inparticular, neutral molecules and atoms) increases, so that the amountof power absorption increases accordingly (by actual resistance). Asdescribed above, as measurement precision for an absorption frequencybecomes lowered, measurement precision for electron density becomeslowered.

In contrast, referring to the frequency characteristics of thereflection coefficient, that is, the frequency characteristics of theimaginary part Γ_(i) of the complex reflection coefficient obtained bythe present invention, the points at which the value of Γ_(i) is zero(zero-crossing point) are remarkable at 800 mTorr (FIG. 10) and 1600mTorr (FIG. 11) as well as 15 mTorr (FIG. 9) and the resonance frequencyf_(p) can be simply and accurately read.

Under the condition of a pressure of 15 mTorr (FIG. 9), the resonancefrequency f_(p) and the electron density calculated at the zero-crosspoint of the imaginary part Γ_(i) of the complex reflection coefficientare 3700 MHz and 8.19×10¹¹, respectively, and the absorption frequencyand the electron density calculated at the minimum peak of the absolutevalue |Γ| are about 3700 MHz and about 8.19×10¹¹, respectively. Underthe condition of a pressure of 800 mTorr (FIG. 10), the resonancefrequency f_(p) and the corresponding electron density are 2550 MHz and3.89×10¹¹, respectively, and the absorption frequency and thecorresponding electron density are about 2500 MHz and about 3.73×10¹¹,respectively. Further, under the condition of a pressure of 1600 mTorr(FIG. 11), the resonance frequency f_(p) and the corresponding electrondensity are 2700 MHz and 4.22×10¹¹, respectively, and the absorptionfrequency and the corresponding electron density are about 2500 MHz andabout 3.81×10¹¹, respectively.

Meanwhile, when pressure is far lower than 15 mTorr, the size of the gasmolecule becomes smaller, and therefore, electron density becomes low.When electron density becomes low, the signal intensity of a reflectedwave from plasma is low, an S/N becomes low, and frequencycharacteristics exhibit a broad tendency. In this case, it is difficultto accurately read an absorption frequency by the PAP method. Incontrast, by employing the plasma resonance probe method of the presentinvention, a resonance frequency f_(p) can be accurately read based onthe zero-cross point of the imaginary part Γ_(i) of a complex reflectioncoefficient regardless of the waveform of frequency characteristics.

FIG. 12 shows an example (experimental data) of an electron densitydistribution characteristic obtained under the condition of a highpressure of 2000 mTorr in accordance with the plasma resonance probemethod of the present invention. For this experiment, in a capacitivelycoupled type plasma processing apparatus for plasma CVD, the temperatureof a susceptor was 600° C., high-frequency power of 450 kHz and 800 Wwas applied to an upper (opposite) electrode, and Ar/H₂ gas (1600/1000scm) was used as plasma creation gas. As shown in FIG. 12, it was foundthat electron density N_(e) could be measured with high accuracy atrespective locations in the radial direction even under the condition ofa high pressure of 2000 mTorr.

Further, in the plasma resonance probe method of the present invention,the spatial distribution characteristic of electron density N_(e) in theradial direction of the chamber 10 can be obtained by moving thelocation of the probe portion 52 a, i.e., the measurement location h, inthe insulating pipe 50 in the radial direction in a scanning manner, asshown in FIGS. 4 and 5, and plotting the measurement values of electrondensity N_(e) at respective measurement locations h₁, h₂, . . . , h_(n)on a graph.

In a preferred embodiment of the present invention, the first and secondmeasurement processes can be each performed in batch for all themeasurement locations h₁, h₂, . . . , h_(n). In more detail, in thefirst measurement process, the frequency characteristics (firstfrequency characteristics: Γ₁(f), Γ₂(f), . . . , Γ_(k)(f), . . . ,Γ_(n)(f)) of complex reflection coefficients Γ are sequentially obtainedat predetermined locations h₁, h₂, . . . , h_(n) in the radial directionin the state where plasma PZ does not exist in the chamber 10, as shownin FIG. 4. In this case, the probe portion 52 a is moved in steps fromthe measurement location h₁ at the right of the drawing (starting end)to the measurement location h_(n) at the left of the drawing(terminating end) in such a way that the coaxial cable 52 isintermittently moved by the linear actuator 56 in the direction in whichthe coaxial cable 52 is pulled out from the insulating pipe 50.

In the second measurement process, the frequency characteristics (secondfrequency characteristics: r₁(pf), Γ₂(pf), . . . , Γ_(k)(pf), . . . ,Γ_(n)(pf)) of complex reflection coefficients Γ are sequentiallyobtained at the locations h₁, h₂, . . . , h_(n) identical with those ofthe first measurement process in the radial direction in the state whereplasma PZ is created in the chamber 10, as shown in FIG. 5. In thiscase, the probe portion 52 a is moved in steps from the measurementlocation at the right of the drawing h₁ (starting end) to themeasurement location h_(n) at the left of the drawing (terminating end)in such a way that the coaxial cable 52 is intermittently moved by thelinear actuator 56 in the direction in which the coaxial cable 52 ispulled out from the insulating pipe 50.

After the first and second frequency characteristics Γ(f) and Γ(pf) havebeen obtained respectively in batch, a batch process for all themeasurement locations h₁, h₂, . . . , h_(n) is performed in each ofsubsequent signal processing steps, i.e., the normalization of thefrequency characteristics Γ(f) and Γ(pf), the extraction of theimaginary part Γ_(i), and the calculation of the resonance frequencyf_(p) and electron density N_(e).

As described above, in accordance with the method in which themeasurements of the reflection coefficients in a plasma OFF state and aplasma ON state are each performed in batch for the entire locations h₁,h₂, . . . , h_(n), the switching of ON and OFF is performed only onceregardless of the number of measurement locations, so that the entiremeasurement efficiency is high, and therefore, measurement time permeasurement location can be shortened to several seconds. In contrast,in the conventional PAP method, the ON/OFF of plasma must be repeatedwhenever a measurement location changes, so that several minutes arerequired for each measurement location. As the number of measurementlocations increases, such a difference in measurement efficiency ormeasurement time becomes remarkable (in particular, in a large diameterchamber).

In the present embodiment, the insulating pipe 50 is hung between a pairof supports (through holes 10 a) provided at opposite locations on thesidewalls of the chamber 10, and is airtightly secured by the O-rings58. The positioning of the probe portion 52 a is performed by moving thecoaxial cable 52 in the insulating pipe 50, which is horizontally fixedlike a bridge, in the axial direction. In this way, the probe portion 52a can be rapidly and accurately positioned at desired locations and beplaced on a horizontal line, so that the reproducibility of measurementlocations can be assured.

Further, since there is no friction between the insulating pipe 50 andthe O-rings 58, the stability of the probe mechanism is increased andcosts of consumables (CoC) is improved without the damage anddeterioration of the O-rings 58. Furthermore, the influence(disturbance) of the probe mechanism on plasma is constant regardless ofa measurement location, and reliability on measurement precision isimproved because disturbance time (measurement time) is very short.

Furthermore, the insulating pipe 50 has a coaxial pipe structure that isconstant or uniform at any location when viewed from the probe portion52 a of the coaxial cable 52. Since the coupling of an electromagneticwave, which is generated from the probe portion 52 a, with plasma isconstant, noise is hardly generated, so that measurement with highprecision and reproducibility can be performed. The bead-shaped ferritemembers 66 as an electromagnetic wave absorber are mounted around thecoaxial cable 52, so that, even when standing wave noise is generated onthe outer conductor (ground portion) 52 b of the coaxial cable 52, itcan be sufficiently eliminated through the effective absorption of thestanding wave noise by the bead-shaped ferrite members 66.

Further, in the plasma electron density measurement apparatus, the outerconductor (ground portion) 52 b of the coaxial cable 52 is groundedthrough the grounding conductor 62 and the chamber 10. By employing thisRF shield function using the chamber 10, the leakage of the RF noise tothe atmosphere or the measuring circuit 54 is effectively prevented, sothat safety for the human body or measurement equipment can be assuredand the malfunction of surrounding electronic equipment, such as a gasdetector, can be avoided.

Furthermore, since, through the use of this RF shield function, noisesignals propagate on the outer conductor (grounding portion) 52 b of thecoaxial cable 52 at an inner area (probe portion 52 b side) when viewedfrom a location where the outer conductor 52 b is connected with thegrounding conductor 62 or a short circuit point A, the bead-shapedferrite members 66 for absorbing standing wave noise are preferablyarranged at a point inner than the short circuit point A. Morepreferably, like the present embodiment, the bead-shaped ferrite members66 may be arranged near the short circuit point A, which is theabdominal portion of the standing wave noise, as much as possible.

In the present embodiment, the coaxial cable 52 is effectively cooled byopening the front end side of the insulating pipe 50, i.e., the side ofthe insulating pipe 50 opposite to the probe portion 52 a, and flowingair into the opening from the cooling gas supply unit 80, so thatthermal expansion and thermal deterioration around the probe portion 52a can be prevented, thus improving the durability thereof.

The plasma electron density measurement method and apparatus of thepresent embodiment allow reliable plasma electron density measurement tobe easily, efficiently and rapidly performed even by using a 300 mmwafer or FPD processing apparatus having a large diameter chamber.

Furthermore, since the present invention enables electron density to beaccurately measured even at a place where plasma density is low, asdescribed above, the monitoring of plasma can be performed at ameasurement location that the plasma is not disturbed. FIG. 13 shows anembodiment of the present invention that enables no-disturbance plasmamonitoring. In this drawing, elements having same configurations andfunctions as those of FIG. 1 are designated by same numerals.

As shown in FIG. 13, in the plasma electron density measuring apparatusof the present embodiment, probe units 100, 102 and 104 are embedded atthree locations, i.e., in the sidewall of the chamber 10, the centralportion of the upper electrode 24 and the peripheral portion of thelower electrode 16. All of the probe units are arranged around theplasma region, so that electron density therearound can be measuredwithout the disturbance of the plasma PZ.

FIGS. 14A and 14B show examples of a probe unit 100 embedded in thesidewall of the chamber. The configuration of FIG. 14A is formed byclosing the front end of the insulating pipe 50 of the above embodiment(FIG. 1) and somewhat projecting the insulating pipe 50 from thesidewall of the chamber 10 toward the plasma region. To improve thedirectionality of radiation toward the front of the probe portion 52 a(plasma region), it is preferable to attach the front of the probeportion 52 a to the front end of the insulating pipe 50.

The configuration of FIG. 14B is formed by bringing a cylindricalhousing 106 made of insulator to be leveled with or lower than the innersurface of the sidewall of the chamber 10. It is preferable, for theimprovement of measurement sensitivity, to provide a window member 108,which is made of a high-permittivity material such as sapphire and issmall in plate thickness, in the front portion of the housing 106.Furthermore, as shown in this drawing, the discontinuous point ofimpedance may be formed in the probe portion 52 a by bending the frontof the probe portion 52 a in an L shape, such that a wave can beefficiently irradiated from the discontinuous point to the frontthereof.

Additionally, to improve front directionality, it is possible to attacha disk-shaped capacitive coupling member 110 to the front of the probeportion 52 a, as shown in FIG. 15B, and to attached a cross-shapedinductive antenna member 112 to the front of the probe portion 52 a, asshown in FIG. 15D. Furthermore, the probe configuration of FIG. 15A isadopted by the probe unit 100 of FIG. 14A, and the probe configurationof FIG. 15C is adopted by the probe unit 100 of FIG. 14B. The probeunits 102 and 104 around the electrode may have the same configurationand function as the probe unit 100.

In FIG. 13, the respective probe units 100, 102 and 104 are connected toa network analyzer 68 through the selection switch 114. During plasmaprocessing, the selection switch 114 is switched to the respective probeunits 100, 102 and 104 in a time division manner under the control ofthe measurement control unit 74, so that the simultaneous measurement ofplasma density in the chamber 10 at a plurality of monitoring locationscan be efficiently performed using a single measuring unit 54. Further,the variations of plasma electron density or the actual situation of theprocess can be simply monitored at a location around the plasma PZwithout disturbing the plasma PZ in the chamber 10 during the process.It is possible to feed back measurement results to a current processcondition or next process condition by transferring informationmonitored by the measuring unit 54 to a main control unit 20. Asrepresentative parameters to monitor the plasma processing, there arepressure, RF power, a gas flow rate, temperature, etc.

In an embodiment shown in FIG. 16, a plasma processing system iscomposed of a plurality of plasma processing apparatuses in accordancewith the embodiment of FIG. 13. As shown in this drawing, probe units116 and 118 embedded in two (three or more are possible) plasmaprocessing apparatuses, respectively, can be connected to a commonvector network analyzer 68 in a time division manner through the use ofa selection switch 114. In this system, it is possible to feed backmeasurement results to a current process condition or next processcondition of the respective processing apparatuses by transferringinformation monitored by the respective processing apparatuses from themeasuring unit 54 to the process control units 20. If the plurality ofplasma processing apparatuses are of the same type, it can be determinedwhether there exists any difference between the processing apparatuses.

An application to which the embodiment of FIG. 13 can be applied is aseasoning. As well known to those skilled in the art, the seasoning is aprocess of repeating a plasma etching cycle (pilot operation) anappropriate number of times using a dummy wafer so as to stabilize theinside of the chamber to be suitable for the atmosphere of processingconditions after the cleaning of the chamber or the replacement ofparts. In general, immediately after the cleaning of a chamber ordisplacement of a part, the attachment of deposits from a plasma spaceto the inner wall of the chamber is greater than the discharge ofdeposits from the inner wall of the chamber to the plasma space, so thatprocessing is not stabilized. While the plasma processing cycle is beingrepeated several number of times, the attachment and discharge ofdeposits are balanced, thus stabilizing the processing.

Conventionally, an etching rate is monitored in each processing cycleunder standard recipe conditions, the number of dummy wafers (or thenumber of pilot cycles and pilot operation time) required until theetching rate is stabilized is determined as a seasoning condition, andthe seasoning condition is fixed and applied to every processing recipe.However, as well known in the art, the fixed seasoning condition is notappropriate for every processing recipe, and may be excessive orinsufficient for some processing recipes. That is, if the seasoningcondition is excessive, an unnecessary etching cycle is performed, tothereby cause a reduction in throughput. In other words, if theseasoning condition is insufficient, unstable processing is performed ona normal wafer, thus causing a reduction in yield. Further, though amethod of setting seasoning conditions based on the experience andfeeling of a process engineer or operator is being performed, certaintyand universality are low, and therefore, the above-mentioned problemsmay arise. In accordance with the present invention, as described below,adaptive seasoning control is performed for each processing recipe, sothat tradeoff between the improvements of throughput and yield can besolved.

In accordance with the plasma resonance probe method of the presentinvention, electron density can be accurately measured even in the spacewhere plasma density is low, so that electron density can be monitoredduring an actual process without disturbing the plasma, e.g., by placingthe probe unit 100 in the sidewall of the chamber 10, as describedabove. After the cleaning of the chamber or the replacement of parts inactual processing, such as plasma etching, an etching rate is highest inan initial etching cycle (first wafer), the etching rate graduallydecreases, while the etching cycle is being repeated, and is finallystabilized after specific cycles. FIG. 17 shows an example in which anetching rate is gradually decreased and, thus, stabilized at respectivelocations on a wafer in the etching cycles of seasoning. The illustratedexample shows a result of a silicon dioxide film etching process, andits basic etching conditions are as follows:

wafer diameter: 200 mm

gas pressure: 15 mTorr

distance between upper and lower electrodes: 25 mm

etching gas: C₅F₈/O₂/Ar=15/380/19 sccm

RF power: upper/lower=2170/1550 W

As shown in FIG. 17, an etching rate E/R changes (decreases)considerably between a first wafer No. 1 and a third wafer No. 3,changes (decreases) still considerably between the third wafer No. 3 anda fifth wafer No. 5, and changes little (decreases) between the fifthwafer No. 5 to a seventh wafer No. 7. In this example, it can beconsidered that seasoning has been completed at the time of processingthe fifth wafer No. 5. Meanwhile, as for the surface of a wafer, theetching rate E/R changes most considerably on the center portion of thewafer, and the etching rate E/R changes meaningfully on the edge portionof the wafer.

FIG. 18 shows a situation in which the average value of an etching rateon a wafer (Ave. E/R) decreases gradually and is stabilized while thefirst to seventh wafer are being processed, and the time variations ofelectron density N_(e) in respective etching cycles. In this case, theelectron density N_(e) was monitored by employing the plasma resonanceprobe method in the vicinity of the sidewall of the chamber (10 mm awayfrom the sidewall of the chamber), and 15 pieces of measurement data areplotted at four-second intervals during each etching cycle [TA=60seconds]. The average value of the etching rate E/R is normalized basedon reference values obtained by processing the first wafer No. 1, andthe electron density N_(e) is normalized based on the average value ofthe values obtained by processing the first wafer No. 1.

As shown in FIG. 18, in the seasoning, it can be appreciated that thereis a relationship between the variations of the etching rate E/Rcorresponding to etching cycles and those of the electron density N_(e).That is, as the number of etching cycles increases to 1, 2, 3, . . . , amaximum value (a value at the initiation of a cycle), a minimum value (avalue at the termination of a cycle) and an average value of theelectron density N_(e) gradually decrease in each etching cycle inconjunction with the gradual decrease of the average value of theetching rates E/R. Subsequently, as the average value of the etchingrates E/R is stabilized, the maximum value, minimum value and averagevalue of electron density N_(e) are also stabilized.

In accordance with the present invention, after the cleaning and partdisplacement in chamber 10, the representative measured values (maximumvalue, minimum value and average value) of time-varying electron densityN_(e) can be monitored with high precision in the vicinity of thesidewall of the chamber 10 in each etching cycle with respect to each ofdummy wafers, which are loaded into the chamber 10 and subject to plasmaetching, without influence on an actual processing. Subsequently, whenthe representative values are stabilized to actual normal values betweentwo continuous processing steps of dummy wafers, seasoning is finished.At this time, a substrate to be put into the chamber 10 and be processedis changed from a dummy wafer to a normal wafer.

In the above-described embodiment, the frequency characteristic of animaginary part Γ_(i) is obtained from the complex reflection coefficientΓ in the vector network analyzer 68 of the measurement unit 54, and aresonance frequency f_(p) is read at the zero-crossing point of theimaginary part Γ_(i). In a modified embodiment, the phase differencebetween incident and reflected waves is measured in the vector networkanalyzer 68, and a resonance frequency f_(p) may be set to a frequencyat the zero-crossing point of the frequency characteristic of the phasedifference. That is, since the sign of the phase difference between theincident and reflected waves measured by the vector network analyzer 68corresponds to that of the imaginary part Γ_(i) of the complexreflection coefficient, a frequency at which the phase differencebecomes zero can be considered as a frequency at which the imaginarypart Γ_(i) of the complex reflection coefficient becomes zero, that is,the resonance frequency f_(p). Accordingly, a high precision measuredvalue of electron density can be obtained from the resonance frequencyf_(p) calculated from the phase difference.

Further, in the above-described embodiment, the probe portion 52 a ofthe coaxial cable 52 is sequentially positioned at respectivemeasurement positions h_(i) in the insulating pipe 50 by intermittentlymoving the probe portion 52 a in steps. However, it is possible that alocation sensor, such as a rotary encoder or linear encoder, is mountedon the linear actuator 54 to detect a current location of the sliderportion 76 or probe portion 52 a, so that the frequency characteristicsof reflection coefficients can be obtained by activating the networkanalyzer 68 when the probe portion 52 a passes through the respectivemeasurement locations h_(k) while continuously moving with uniformvelocity the coaxial cable 52 in the axial direction. It is alsopossible to limit the measurement positions h_(k) to a single locationin the chamber 10.

In the above-described embodiment, the insulating pipe 50 accommodatingthe probe portion 52 a of the coaxial cable 52 is horizontally hungbetween a pair of supports (through holes 10 a) provided at oppositelocations on the sidewalls of the chamber 10. However, the plasmaresonance probe method of the present invention can be applied to acantilever scheme where the insulating pipe 50 is supported with thefront end thereof being suspended in space. The actuator 56 of theabove-described embodiment is of a type in which a rotational drivingforce of an electric motor is converted into a rectilinear driving forceby a ball-screw mechanism. However, the actuator used in the presentinvention is not limited to such a motor-type driving device, but may beany driving device such as a pneumatic type or magnetic type device.

Next, with reference to FIGS. 19 to 31, an embodiment of the PAP methodof the present invention is described. In FIG. 19, a configuration of aplasma electron density measurement method and apparatus in accordancewith a second embodiment of the present invention is illustrated. Inthese drawings, elements having same configurations and functions asthose in the plasma processing apparatus and plasma monitoring apparatusof FIG. 1 are assigned the same reference numerals, and detaileddescriptions thereof are omitted.

In the second embodiment, a measuring unit 54 of a plasma densitymeasuring apparatus includes a scalar network analyzer 120 and ameasurement control unit 122 to carry out the PAP method.

The scalar network analyzer 120 transmits an electromagnetic signal(incident wave) having minute power to a probe portion 52 a of a coaxialcable 52 with respect to each frequency while performing frequencysweeping in a band ranging from several hundred MHz to several GHz to beirradiated to plasma PZ in a chamber 10, obtains a scalar reflectioncoefficient based on the ratio of the amount of the power of aelectromagnetic wave (reflected wave) reflected from the plasma PZ tothe amount of the power of an incident wave, and thus obtains thefrequency characteristic thereof. The measurement control unit 122 isadapted to perform control and calculation process for measurement. Inparticular, the measurement control unit 122 obtains the frequencycharacteristic of a scalar reflection coefficient obtained by the scalarnetwork analyzer 120, calculates the minimum peak or absorption peak ofa waveform of the frequency characteristic, and obtains a frequencycorresponding to the absorption peak, that is, a plasma absorptionfrequency.

Now, with reference to FIGS. 20 to 22, a method of measuring a plasmaabsorption frequency and electron density in the plasma monitoringapparatus of the present embodiment is described. As shown in FIG. 20,the plasma monitoring of the present embodiment is divided into threesteps, including setting, batch measurement and batch data processing.

At the setting step (step S1), in the measurement control unit 122,parameters related to monitoring (for example, RF power, pressure, gasspecies, distance between electrodes, and a configuration of theelectrodes) or measurement locations are set and input. For themeasurement locations, the data of respective locations may be directlyset and input. Alternatively, the measurement locations may becalculated based on the set and input values of the location of anorigin, and the number of measurement locations or pitch (intervalbetween the measurement locations).

The batch measurement step includes a first batch measurement step (stepS2) of obtaining the frequency characteristics (first frequencycharacteristics) of reflection coefficients in batch for all themeasurement locations in a plasma OFF state where there is no plasma PZin the chamber 10, and a second batch measurement step (step S3) ofobtaining frequency characteristics of reflection coefficients (secondfrequency characteristics) in batch for all the measurement locations ina plasma ON state where there exists plasma PZ in the chamber 10.

In FIG. 21, the detailed sequence of the first batch measurement step(step S2) is shown. In this first batch measurement step, first, it isdetermined whether the plasma PZ does not exist in the chamber 10 (stepsA1 and A2). From an apparatus point of view, the state without plasmaPZ, that is, the plasma OFF state, can be initiated in such a way thathigh frequency power supplies 18 and 38 stop the output of highfrequency power and a processing gas supply unit 34 stops the supply ofprocessing gas. Furthermore, the pressure of the chamber 10 ismaintained at a certain vacuum degree.

As described above, in the state where the plasma PZ does not exist inthe chamber 10, the frequency characteristics of reflection coefficients(first frequency characteristics) are sequentially obtained for presetmeasurement locations h₁, h₂, . . . , h_(i), . . . , h_(n−1), h_(n) inthe radial direction of the chamber. In more detail, like the firstembodiment (FIG. 1), a probe portion 52 a is positioned at a targetmeasurement location h_(i) (step A3), an electromagnetic signal(examination wave or incident wave) of, e.g., 1 mW is sent from thescalar network analyzer 52 a to the probe portion 52 a of the coaxialcable 52 and irradiated to surroundings (mainly, in the radial directionwhen viewed from the probe portion 52 a) while performing frequencysweeping in a band, e.g., ranging from several hundred MHz to severalGHz. Then, a scalar reflectance or reflection coefficient is obtainedfrom the ratio of the amount of the power of a signal reflected to thescalar network analyzer 120 to the amount of the power of the incidentwave. The frequency characteristic Γi(f) (parameter S11) of thereflection coefficient obtained or displayed by the scalar networkanalyzer 120 is stored in a memory in the measurement control unit 122(steps A4 and A5). Subsequently, the probe portion 52 a is moved to thenext measurement location h_(i+1)(step A6→A7→A8→A3), the frequencycharacteristic Γi+1(f) (parameter S11) of a reflection coefficient isobtained by signal processing as described above (step A4), and theobtained frequency characteristic is stored in the memory in themeasurement control unit 122 as measured data (step A5). Theabove-described series of steps (steps A3, A4 and A5) are repeated forall the measurement locations h₁, h₂, . . . , h_(i), . . . , h_(n−1),h_(n) (steps A6, A7 and A8).

In the present embodiment, by sequentially moving the probe portion 52 ain steps from the measurement location h₁ at the right-hand end(initiation end) of the drawing to the measurement location h_(n)(termination end) at the left-hand end thereof by intermittently movingthe coaxial cable 52 through the use of a linear actuator 56 in thedirection in which the coaxial cable 52 is pulled out from theinsulating pipe 50, as shown in FIG. 4, the series of steps (steps A3,A4 and A5) can be efficiently performed in a short time (within a tacttime of several seconds).

In FIG. 22, a detailed sequence in the second batch measurement step(step S3) is shown. In the second batch measurement step, desired plasmaPZ is created in the chamber 10 first (step B1). From an apparatus pointof view, the state where the plasma PZ exists, that is, a plasma ONstate, can be initiated in such a way that the high frequency powersupplies 18 and 38 apply high frequency power to both electrodes 16 and24 at preset RF power and the processing gas supply unit 34 suppliesdesired processing gas into the chamber 10.

As described above, in the state where the plasma PZ is being created inthe chamber 10, the frequency characteristics of reflection coefficients(second frequency characteristics) are sequentially obtained at the samemeasurement locations h₁, h₂, . . . , h_(i), . . . , h_(n−1), h_(n) asthe first batch measurement step. In more detail, according to the samesequence and signal processing as described above, the probe portion 52a of the coaxial cable 52 is sequentially positioned at respectivemeasurement locations h_(i) by the linear actuator 56 (step B2), thefrequency characteristics Γi(pf) of the reflection coefficients areobtained by the scalar network analyzer 120 for the respectivemeasurement locations h_(i), and the obtained frequency characteristicis stored in the memory in the measurement control unit 122 as measureddata (step B4). Such a series of steps (steps B2, B3 and B4) arerepeated for all the measurement locations h₁, h₂, . . . , h_(i), . . ., h_(n−1), h_(n) (steps B5, B6 and B7).

In the second batch measurement step, as shown in FIG. 5, bysequentially moving the probe portion 52 a in steps from the measurementlocation h₁ at the right-hand end (initiation end) of the drawing to themeasurement location h_(n) (termination end) at the left-hand endthereof by intermittently moving the coaxial cable 52 through the use ofthe linear actuator 56 in the direction in which the coaxial cable 52 ispulled out from the insulating pipe 50, the series of steps (steps B2,B3 and B4) can be efficiently performed within a tact time of severalseconds.

As for the coaxial cable 52, since an outer conductor 52 b is astainless steel pipe having superior rigidity, stable linearity can bemaintained while the coaxial cable 52 is being pulled out from theinsulating pipe 50. Further, the thermal expansion and rupture of aninsulating member 52 c can be prevented in the high temperatureatmosphere of plasma PZ.

In FIG. 20, the batch data processing step includes a first dataprocessing step (step S4) of calculating in batch plasma absorptionfrequencies from the first and second frequency characteristics Γ(f) andΓ(pf) of the reflection coefficients obtained at the batch measurementstep for all the measurement locations h₁, h₂, . . . , h_(n) through acertain operation (for example, division or subtraction), and a seconddata processing step (step S5) of calculating in batch plasma electrondensity through the operation according to Equation 1 based on themeasurement values of the plasma absorption frequencies.

In more detail, in the first data processing step (step S4), the ratioΓi(pf)/Γi(f) of the second frequency characteristic Γi(pf) to the firstfrequency characteristic Γi(f) is calculated for each of the measurementlocations h₁, h₂, . . . , h_(n−1), h_(n). The ratio Γi(pf)/Γi(f)indicates the frequency characteristics of energy absorption by plasmain a vacuum state. Strictly speaking an electromagnetic wave irradiatedfrom the probe portion 52 a propagates along the surface of theinsulating pipe 50, and the absorption of the surface wave occurs whenthe frequency of the surface wave coincides with the number of electronoscillations f_(p) of the plasma, so that reflectance is extremelyreduced. Accordingly, a frequency at a point of time when the ratioΓi(pf)/Γi(f) forms a minimum peak is calculated, which can be used as ameasured value of the plasma absorption frequency.

In the second data processing step (step S5), the measured values ofelectron density N_(e) are obtained for the respective measurementlocations h₁, h₂, . . . , h_(n−1), h_(n) by employing Equation 1 basedon the measured values of plasma absorption frequencies. By plotting themeasured values of the electron density N_(e) on a graph to correspondto the respective measurement locations, the spatial distribution ofelectron density N_(e) in the radial direction of the plasma PZ can beexamined.

FIG. 23 shows an example (embodiment) of the spatial distributioncharacteristics of electron density N_(e) obtained in the plasmamonitoring apparatus of the present embodiment together with acomparative example. In this case, the comparative example is thespatial distribution characteristics of electron density N_(e) that areobtained in such a way as to measure the first and second frequencycharacteristics Γi(f) and Γi(fp) of reflected waves while switching aplasma OFF state to a plasma ON state and vice versa at the respectivemeasurement locations h_(i) in the apparatus of FIG. 19.

As shown in the drawing, in the embodiment and comparative example,there is no great difference between the spatial distributioncharacteristics of electron density N_(e). However, since thecomparative example is based on the method of measuring reflectioncoefficients whenever a plasma OFF state is switched to a plasma ONstate and vice versa at respective measurement locations, and ON/OFFswitching time is consumed in proportion to the number of measurementlocations, the entire measurement efficiency is low, so that ameasurement time of several seconds is required for each measurementlocation. In contrast, since the embodiment is based on the method ofperforming each of the measurements of reflection coefficients in aplasma OFF state and a plasma ON state in batch for all the measurementlocations h_(i) to h_(n), and performs ON/OFF switching only onceregardless of the number of measurement locations, the entiremeasurement efficiency is high, so that measurement time for eachmeasurement location can be shortened to less than several seconds.Accordingly, in the example of FIG. 23 (where the number of measurementpoints is 16), it takes a total measurement time of about 30 minutes inthe comparative example, while the measurement could be finished withinabout 3 minutes in the embodiment. This difference in measurementefficiency or time becomes remarkable as the number of measurementpoints are increased.

As described above, by employing the plasma monitoring apparatus of thepresent embodiment, it is possible to efficiently measure plasmaabsorption frequencies or electron density in a short time, and it isalso possible to easily and efficiently perform highly reliable plasmamonitoring in a short time even when using a 300 mm wafer or FPDprocessing apparatus with a large diameter chamber.

Further, in an actual manufacturing process that a plasma processingapparatus in accordance with the present embodiment performs, it isdesirable to remove a probe mechanism (an insulating pipe and a coaxialcable) from the processing apparatus. In the present embodiment, thethrough hole 10 a of the chamber 10, which is opened when the insulatingpipe 50 is pulled out, may be vacuum-sealed by closing the through hole10 a with a sealing member such as a plug.

In the following, a specific example of the second embodiment will bedescribed.

In the plasma processing apparatus (FIG. 19), the RF frequencies ofupper and lower frequency power (high frequency power supplies 38 and18) were set to 60 MHz and 2 MHz, respectively, and the interval (gap)between the upper electrode 24 and the lower electrode (susceptor) 16was set to 25 mm.

In the plasma monitoring apparatus of the embodiment, as for theinsulating pipe 50, a transparent quartz pipe of 550 mm in total length,3 mm in outer diameter and 1.5 mm in inner diameter was used. Further,the height at which the insulating pipe 50 is hung between both throughholes 10 a of the sidewalls of the chamber 10 was set to a location 10mm away from the upper electrode 24 and 15 mm away from the lowerelectrode 16. As for the coaxial cable 52, a semi-rigid cable SC-086/50(a product of Coax company) of 0.20 mm in the outer diameter of a corewire (inner conductor) 52 a, 0.86 mm in the outer diameter of an outerconductor 52 b and a characteristic impedance of 50 Ω was used. Further,the probe portion was formed by exposing a portion of the core wire 52 aat the front end thereof to which Teflon® is attached. As for themeasuring circuit 54, a high pass filter of Japanese High Frequencycompany was used as the HPF 72, 11930B of Agilent Technology company wasused as the RF limiter 70, and HP8753ET of Agilent Technology companywas used as the scalar network analyzer 120. The scalar network analyzer120 was set to sweep and output high frequency signals (0 dBm: 1 mW) ina band ranging from 150 to 2500 MHz at every 600 msec. A linear actuatorLCA40 of THK company was used as the linear actuator 56.

In the plasma absorption probe method of the embodiment, the groundingline 52 b of the coaxial cable 52 is short-circuited and grounded to thehousing (sidewall) of the chamber 10 so as to cope with an RF leakage.However, in a configuration without the bead-type ferrite member 66,when the insertion length L of the coaxial cable 52 into the chamber 10(distance between the short-circuited point A and the front end of theprobe portion 52 a) was changed, there was a phenomenon in which peaks,which were considered noise other than a plasma absorption frequency,were periodically generated.

To clarify the mechanism of the noise generation, the insertion length L(FIG. 2) of the coaxial cable 52 was changed and the frequencycharacteristics of noise peaks obtained at this time were investigated.FIG. 24 shows these frequency characteristics. It can be appreciatedfrom FIG. 24 that noise peaks are periodically generated in a band above1500 MHz in accordance with the insertion length L of the coaxial cable52. Further, the plasma frequency f_(p) exists in a range ranging from1000 MHz to 1500 MHz.

In FIG. 25, the frequencies (measured values) of noise peaks arerepresented by points, while resonance frequencies (calculated values ofpeak frequencies) determined by the insertion lengths L are representedby curves. In FIG. 25, λ represents a wavelength of a noise signalpropagating along the outer conductor 52 b of the coaxial cable 52, andλg represents a wavelength of a noise signal propagating along the corewire (inner conductor 52 a). It can be found from the graph of FIG. 25that the measured values of noise peaks almost completely coincide withthe calculated values thereof (integer times a half wavelength).

It is appreciated from these results that standing waves are generatedby the grounding line 52 b of the inserted coaxial cable 52, thesestanding waves are recognized as signals by the probe portion, andstanding wave noise peaks other than absorption peaks attributable toplasma are generated. If such standing waves are generated, the S/N ofthe frequency characteristics of plasma absorption is deteriorated andmay be erroneously considered as plasma absorption peaks.

Accordingly, as in the above-described embodiment, experiments on theabsorption of standing wave noise using an electromagnetic wave absorber66 were carried out. A bead ferrite HF70BB3.5×5×1.3 of TDK company wasused as the electromagnetic wave absorber 66. Further, for the plasmacreation conditions in the plasma processing apparatus, C₅F₈/Ar/O₂ mixedgas (flow rate: 15/380/19 sccm) was used as processing gas, the pressureof the chamber 10 was set to 2.0 Pa (15 mTorr), upper/lower highfrequency powers were 2.17/1.55 kW, respectively, and the temperaturesof an upper electrode/sidewall of chamber/lower electrode were set to60/50/20° C., respectively. Two points where R=0 (wafer center) andR=160 mm were selected as measurement locations, where R is the distancefrom the center of a wafer.

FIGS. 26A and 26B show data on the results of these experiments. As canbe known from the results of these experiments, it were clearlyascertained that standing wave noise could be effectively eliminatedwithout influence on original plasma absorption peaks by mounting theelectromagnetic wave absorber 66 on the coaxial cable 52.

Next, noise reduction effect under plasma cleaning conditions wasestimated by experiments. The purpose thereof is to ascertain whetherstanding wave noise can be effectively reduced by the electromagneticwave absorber 66 under the conditions in which electron density isreduced and S/N is deteriorated like in the plasma cleaning conditions.Herein, the plasma cleaning means a cleaning method of eliminatingreaction residues attached to the inner wall of the chamber etc. byusing plasma.

For the plasma creation conditions in the plasma processing apparatus,O₂ was used as the processing gas, the flow rate of supply thereof wasset to 200 sccm, the pressure of the chamber 10 was set to 2.0 Pa (15mTorr), lower power was set to 200 W, the temperatures of an upperelectrode/sidewall of chamber/lower electrode were 30/50/20° C.,respectively, and the lower power was changed from 1500 W to 200 W. Themeasurement location was set to a location where R=0 (wafer center).

FIG. 27 shows the results of these experiments. It could be alsoappreciated that, since only standing wave noise could be selectivelyeliminated, plasma absorption peak could be detected even when it is aweak signal.

Further, the variations of a signal were estimated when theelectromagnetic wave absorber 66 mounted on the coaxial cable 52 wasenhanced. Specifically, the signals (depths) of plasma absorption peaks,which were obtained when the number of bead ferrites (HF70BB3.5×5×1.3)arranged in series to the coaxial cable 52 was increased to 5, 10 and15, respectively, were compared with each other. As a result, as shownin FIG. 28, it was found that signals increases as the number of beadferrites increases. It is considered that the reason for this is thatthe ferrites eliminate noise components contained in the signals throughelectromagnetic induction. However, if an electromagnetic wave isabsorbed by a ferrite, the electromagnetic wave is converted intothermal energy, so that the ferrite itself is heated. When thetemperature of the ferrite exceeds the Curie point (Tc: about 100° C.),the ferrite loses the characteristic of electromagnetic wave absorption.Accordingly, it is preferable to cool the ferrite. In this embodiment,the electromagnetic wave absorber 66 is air-cooled by the cooling gassupply unit 80.

Further, a relationship between pressure and the spatial distribution ofelectron density was investigated for several processing plasmas asfollows.

(1) The spatial distribution of electron density along the radialdirection of the chamber was investigated for etching plasma used toform a connection hole having a high aspect ratio, with pressure beingused as a parameter. FIG. 29 shows results thereof. The basic plasmacreation conditions (recipe) were as follows:

wafer diameter: 200 mm

etching gas: C₅F₈/Ar/O₂ mixed gas

gas flow rate: C₅F₈/Ar/O₂=15/380/19 sccm

gas pressure: 2.0˜26.6 Pa (15˜200 mTorr)

RF power: upper/lower=2.17/1.55 kW

set temperature: upper electrode/sidewall/lower electrode=60/50/20° C.

amplitudes of lower RF voltages: 1385 V (2.0 Pa), 1345 V (4.0 Pa), 1355V (10.6 Pa), 1370 V (16.0 Pa), 1380 V (26.6 Pa)

As shown in FIG. 29, it can be found that, under these plasma creationconditions, if the pressure exceeds 16.0 Pa (120 mTorr), electrondensity N_(e) decreases at a location around the center of a wafer, sothat uniformity is lost.

(2) The spatial distribution of electron density along the radialdirection of the chamber was investigated for etching plasma used toform a wiring groove (trench) on a Si substrate, with pressure beingused as a parameter. FIG. 30 shows results thereof. The basic plasmacreation conditions (recipe) were as follows:

wafer diameter: 200 mm

etching gas: CF₄/O₂ mixed gas

gas flow rate: CF₄/O₂=40/3 sccm

gas pressure: 6.7˜66.5 Pa (50˜500 mTorr)

RF power: upper/lower=1.0/1.2 kW

set temperature: upper electrode/sidewall/lower electrode=60/50/20° C.

amplitudes of lower RF voltages: 1530 V(6.7 Pa), 1690 V (20.0 Pa), 1400V (39.9 Pa), 1180 V (66.5 Pa)

As shown in FIG. 30, it can be found that, under these plasma creationconditions, electron density N_(e) has a non-uniform distribution at agas pressure of 6.7 Pa or 20.0 Pa but a uniform distribution at apressure above 39.9 Pa.

(3) The spatial distribution of electron density along the radialdirection of the chamber was investigated for etching plasma used toform a via hole in an interlayer insulating film on a substrate, withpressure being used as a parameter. FIG. 31 shows results thereof. Thebasic plasma creation conditions (recipe) were as follows:

wafer diameter: 200 mm

etching gas: N₂ gas

gas flow rate: 300 sccm

gas pressure: 53.2˜106.4 Pa (400˜800 mTorr)

RF power: upper/lower=1.5/1.0 kW

set temperature: upper electrode/sidewall/lower electrode=30/50/20° C.

amplitudes of lower RF voltages: 1015 V (53.2 Pa), 938 V (106.4 Pa)

As shown in FIG. 31, it can be found that, under these plasma creationconditions, the uniformity of electron density N_(e) can be maintainedeven when gas pressure is increased to 106.4 Pa.

As described above, in the plasma monitoring method and apparatus of thepresent embodiment, the measurement of high precision electron densitycan be performed over a wide range of low pressure to high pressure in ashort time. Accordingly, the plasma processing apparatus of the presentembodiment optimizes a recipe so that plasma density, i.e., electrondensity, are uniformly distributed in a processing space under desiredprocessing conditions, thus assuring the in-surface uniformity of plasmaprocessing and improving yields.

Furthermore, in the second embodiment, various modifications arepossible as in the first embodiment.

EMBODIMENT 3

Next, with reference to FIGS. 32 to 48, an embodiment of the plasmalight emission measuring method of the present invention is described.FIG. 32 shows a configuration of a plasma processing apparatus to whichplasma light emission measuring method and apparatus in accordance witha third embodiment of the present invention are applied. In thesedrawings, elements having same configurations and functions as those inthe plasma processing apparatus and plasma monitoring apparatus of FIG.1 are assigned same reference numerals, and detailed descriptionsthereof are omitted.

The plasma light emission measuring apparatus of the present embodimentincludes a cylindrical transparent insulating pipe 50 fixedly attachedto a chamber 10, a rod-shaped optical transmission probe 130 providedwith a light receiving surface 130 a at a front end thereof and insertedinto a quartz pipe 50 through one end of the quartz pipe 50 (left-handside of FIG. 1) to slide therethrough, a measurement unit 132 formeasuring light emission from plasma PZ created in the chamber 10through the probe 130, a linear actuator 56 for moving the probe 130 inan axial direction thereof, and a flexible bundle fiber 134 foroptically connecting the probe 130 to the measurement unit 132.

The transparent insulating pipe 50 is made of a transparent andheat-resistant insulating material, e.g., quartz or sapphire, somewhatlonger than an outer diameter of the chamber 10, rectilinearly(linearly) formed, and open at both ends thereof.

The front end of the probe 130, as illustrated in FIG. 33, is mountedwith a light shielding type cylindrical cap 136 made of, e.g., stainlesssteel (SUS). A cylindrical body 138 made of, e.g., stainless steel isaccommodated in the cap 136. A section 140 of the cylindrical body 138facing the light receiving surface 130 a of the probe 130 forms a mirrorinclined by 45° with respect to the axial direction. A circular openingor window 142 is formed in the sidewall of the cap 136 at a locationpositioned in the reflection direction of the mirror 140 when viewedfrom the light receiving surface 130 a of the probe 130. The lightentering the window 142 from a location in front of the window 142 isreflected by the mirror 64, and is incident on the light receivingsurface 130 a of the probe 130. As described above, in the presentembodiment, a light collecting unit 144 for collecting plasma light inthe chamber 10 to have high directionality is formed by employing thewindow 142, the mirror 140 and the light receiving surface 130 a of theprobe 130.

The probe 130 is formed of a quartz rod of, e.g., several mm or less indiameter. The probe 130 confines light incident on the light receivingsurface 130 a at the front end thereof while totally reflecting thelight by the boundary surface or surrounding surface thereof, transmitsthe light to the other end thereof, and irradiates the light through thesurface of the other end thereof. As the quartz rod, a rod made ofhydrous synthetic quartz, which exhibits a high transmissioncharacteristic and does not emit fluorescence, is preferably used in acase where wavelengths ranging from 200 nm to 900 nm used for thegeneral spectroscopy of plasma light emission are required. Meanwhile,in the measurement of a wavelength range of a near infrared ray to amiddle infrared ray (900 nm˜), anhydrous synthetic quartz or fusedquartz that exhibits a high transmission characteristic in thewavelength range is preferably used as the rod material. To efficientlyperform the measurement of a wide wavelength range of an ultraviolet rayto an infrared ray, sapphire may be used as the rod material.

The probe 130, as described above, sufficiently performs lighttransmission with only a single body of quartz rod. However, to preventfaint light from entering the side surface of the quartz rod, the sidesurface or surrounding surface of the rod may be preferably surroundedwith a cladding 146, as shown in FIG. 34A. More preferably, as shown inFIG. 34B, the surrounding surface of the cladding 146 (or the quartz rod130) may be surrounded with a light shielding coating, e.g., a blackpaint 148.

The measurement unit 132 is an apparatus for measuring the lightemission of plasma in the chamber 10 using spectroscopic analysisthrough the probe 130. The measurement unit 132 includes a spectroscope150 for dissolving or dividing light from the probe 130 into a spectrum,a photoelectric conversion unit 152 for converting a spectrum of acertain frequency obtained from the spectroscope into an electricalsignal, a measurement operation unit 154 for obtaining the intensity ofa spectrum corresponding to the output signal of the photoelectricconversion unit 152, and a measurement control unit 156 for controllingmeasurement-related units. For example, a prism or diffraction gratingmay be used as the spectroscope 150. An optical filter instead of thespectroscope may be used. For example, a photomultiplier tube orphotodiode may be used as the photoelectric conversion unit 152.

The bundle fiber 134 is formed by binding a plurality of flexibleoptical fibers, one end of which is optically connected to one end ofthe probe 52 via a connector 158, and the other end of which isoptically connected to the spectroscope 150 of the light emissionmeasurement unit 132. The connector 158 connects the bundle fiber 134 tothe probe 130, e.g., in an end-to-end manner.

Hereinafter, the operation of the plasma light emission measuringapparatus of the present embodiment is described. In the plasma lightemission measuring apparatus, the probe 130 is moved within the quartzpipe 50 in the axial direction thereof, that is, the radial direction ofthe chamber 10 by the rectilinear operation of the linear actuator 56 soas to measure light emission from plasma PZ created in the chamber 10.In general, the light receiving surface 130 a of the probe 130 isinserted into an inner side of the quartz pipe 50 up to a location overthe farthest measurement location when viewed from the linear actuatorside, and is rectilinearly moved in the direction of pulling the probe130 during measurement. With this rectilinear movement in the axialdirection, the light collecting unit 144 of the probe 130 scans a plasmaspace in chamber 10 in the radial direction thereof, and collects plasmalight at respective locations in the radial direction. In more detail,as shown in FIG. 33, light generated from the plasma PZ at a higherlocation enters the quartz pipe 50 and is incident on the mirror 140through the window 142 of the cap 136 at respective locations on a scanline, and light reflected by the mirror 140 is incident on the lightreceiving surface 130 a of the probe 130. Although, in the example shownin the drawing, plasma light is collected from a location above theprobe 130, plasma light may be collected from any location such aslocations below and beside the probe 130 as well as a location above theprobe 130 depending on the orientation of the mirror 140.

The plasma light incident on the light receiving surface 130 a of theprobe 130 propagates within the probe 130, is irradiated in theconnector 158 toward the other end surface of the probe 130, and isincident on one end surface or light receiving surface of the bundlefiber 134. The plasma light incident on the light receiving surface ofthe bundle fiber 134 propagates within the bundle fiber 134, and isirradiated from the other end surface of the bundle fiber 134, andenters the spectroscope 150 of the measurement unit 132.

In the measurement unit 132, the spectroscope 150 extracts a spectrumfrom the received plasma light. The photoelectric conversion unit 152converts the spectrum extracted by the spectroscope 150 into, e.g., anoptical current, and outputs a voltage signal corresponding to theintensity of the spectrum. The measurement operation unit 154 obtains ameasured value of the intensity of the spectrum from the level of thevoltage signal obtained by the photoelectric conversion unit 152. Sincethe light collecting unit 144 is allowed to scan in the radial directionof the chamber 10 by moving the probe 130 within the quartz pipe 50 inthe radial direction thereof using the linear actuator 56 as describedabove, the intensity of plasma light or spectrum can be measured atrespective locations on a scan line. Furthermore, by mounting a positionsensor such as a linear encoder or rotary encoder on the linear actuator56, the location of the light collecting unit 144, i.e., a measurementlocation, can be detected. The measured values of the intensity ofspectra at the respective locations are stored in a memory of themeasurement operation unit 154 or measurement control unit 156 as plasmalight emission measurement data, are displayed or printed as spatialdistribution characteristics (graph) by a display device or printer (notshown) or used for a required monitoring analysis.

As described above, in the plasma light emission measurement apparatus,the quartz pipe 50 is inserted into the chamber 10, the rod-shapedoptical transmission probe 130 is moved within the quartz pipe 50 in theradial direction thereof, the emitted light of the plasma PZ iscollected by the light collecting unit 144 of the probe 130 at certainmeasurement locations in the axial direction, the collected plasma lightis transmitted to the measurement unit 132 through the probe 130 and thebundle fiber 134, and measured values of a certain characteristic or anattribute (for example, the intensity of a certain wavelength spectrum)are obtained by the measurement unit 132 with respect to plasma light atthe respective measurement locations.

In this case, since the quartz pipe 50 and the probe 130 are insulatingmaterial, i.e., nonmetal, there is no concern for the disturbance of theplasma PZ and highly reliable and precise spatial distributionmeasurement can be performed on plasma light emission, even though theyare inserted into capacitively coupled plasma PZ created betweenparallel flat plate electrodes 16 and 24. Furthermore, in thisembodiment, the cap 136 and mirror 140 of the light collecting unit 144are made of metal (SUS) and the entire length of the metallic member isseveral cms, they cannot perform an antenna function, so that they donot influence high frequency discharge between the parallel flat plateelectrodes 16 and 24.

Furthermore, in the present embodiment, the quartz pipe 50 ishorizontally hung between a pair of supports (through holes 10 a)provided at the opposite locations of the sidewalls of the chamber 10,and the probe 130 is moved within such a bridge-type quartz pipe 50(using the quartz pipe 50 as a guide member) in the axial directionthereof, so that the scanning of the probe can be realized stably at ahigh-speed on a certain horizontal line in the radial direction of thechamber. In this way, even in a short processing time of, e.g., aseveral minutes, the above-described spatial distribution measurementcan be repeated a plurality of times at regular intervals and resolutionmeasurement can be performed in a time axis direction.

Furthermore, in the present embodiment, by providing plasma lightcollected by the probe 130 in the chamber 10 to the spectroscope 150 ofthe measurement unit 132 through the bundle fiber 134 outside thechamber 10, plasma light emission in the chamber 10 can be collected ata desired viewing angle.

With reference to FIG. 35, the optical functions of the probe 130 andthe bundle fiber 134 are described. In the chamber 10, light emissionfrom the plasma PZ passes through the window 142 of the cap 136, isreflected by the mirror 140, and is incident on the light receivingsurface 130 a of the probe. In this case, the plasma light is incidenton the light receiving surface 130 a of the probe 130 actually at aviewing angle of ±90° (NA=1) regardless of a unique numerical apertureN/A of the probe 130. Additionally, the plasma light is irradiated fromthe other end surface of the probe 130 actually at a viewing angle of±90°, which is symmetrical with the light receiving side of the probe130. As a result, the plasma light is incident on the light receivingsurface 134 a of the bundle fiber 134, which is actually a samesituation as on the light receiving surface 130 a of the probe 130. Thebundle fiber 134 receives the plasma light at a unique numericalaperture (NA<1), the other end surface 134 b irradiates the plasma lightat a unique numerical aperture (NA<1). In this way, plasma light can becollected with a directionality equivalent to that of a case where thelight receiving surface 134 a of the bundle fiber 134 is put into thechamber 10.

Meanwhile, if the bundle fiber 134 is put into the chamber 10, theprotective tube (generally, made of metal) thereof is electricallycoupled with plasma PZ, so that the plasma PZ may be disturbed. In thepresent embodiment, since the bundle fiber 134 exists outside thechamber 10, it does not influence the plasma PZ.

Further, the bundle fiber 134 has an advantage in that it is easy to bealigned with the probe 130 in the connector 158 compared to a singleoptical fiber, in addition to the above-described directionality.

Meanwhile, if the diameter of the rod of the probe 130 is increased,undesired light ML directly incident on the light receiving surface 130a from a front location without passing through the mirror 140 as wellas original light PL incident from a location in front of the window142, reflected by the mirror 140 and incident on the light receivingsurface 130 a of the probe 130 may be mixed in the collected plasmalight collected by the light collecting unit 144, as shown in FIG. 36.In order to solve this problem, as shown in the drawing, one end of theprobe 130 is preferably formed of a light receiving surface slantinglycut at a certain angle θ so that a normal line N of the light receivingsurface 130 a of the probe 130 is slanted with respect to the axialdirection toward the window side at the angle θ. With thisconfiguration, even though the undesired light ML is incident on thelight receiving surface 130 a of the probe 130 from a front location,the light is incident at an angle larger than the numerical aperture NAof the bundle fiber 134, so that the frontal light can be eliminated.

FIG. 37 shows the optimal cut angles θ of the light receiving surface ofthe quartz rod used in the probe 130 with respect to the refractiveindices thereof on a graph, with numerical apertures being used as aparameter. Since the refractive index of the quartz rod varies with thewavelength of light, a cut angle θ may be determined based on theshortest wavelength of a spectrum to be measured in an actualapplication. For example, in case of using a quartz rod having anumerical aperture of 0.22, when a refractive index corresponding to theshortest spectrum to be measured is 1.453, the cut angle θ may be set to26.8° based on the graph of FIG. 37.

As described above, in accordance with the plasma light emissionmeasuring apparatus of the present embodiment, light emission from theplasma can be measured or spectroscopically analyzed in view of aspatial distribution in the radial direction of the chamber withoutinfluence on a plasma distribution within the chamber 10. Accordingly, acorrelation between the intra-surface distribution of processing resultsand the spatial distribution of plasma light emission can be interpretedwith high precision.

FIGS. 38A to 40B show an example of a correlation between theintra-surface distribution of the etching rates and the spatialdistribution of plasma emission in an application in which the plasmaprocessing apparatus of the present embodiment is applied to perform aplasma etching.

FIGS. 38A and 38B show the correlation between the intra-distribution ofetching rates E/R of SiO₂ (FIG. 38A) and the spatial distribution of Arradical light emission I [Ar] (750 nm: 13.48 eV) (FIG. 38B) in two typesof silicon dioxide (SiO₂) film etching A and B with the resistivities ofupper electrodes 24 being different.

FIGS. 39A and 39B show the correlation between the intra-distribution ofetching rates E/R of SiO₂ (FIG. 39A) and the spatial distribution of Arradical light emission I[Ar](750 nm: 13.48 eV) (FIG. 39B) in two typesof silicon dioxide (SiO₂) film etching C and D with the structures ofupper electrodes 24 being different.

FIGS. 40A and 40B show the correlation between the intra-distribution ofetching rates E/R of photoresist (FIG. 40A) and the spatial distributionof Ar radical light emission I[Ar]/F radical light emission I[F] (704nm: 14.75 eV) (FIG. 40B) in two types of silicon dioxide (SiO₂) filmetching C and D with the structures of upper electrodes 24 beingdifferent.

FIGS. 41 to 43 show a configuration and an operation of a plasmaprocessing apparatus to which plasma light emission measuring method andapparatus according to another embodiment (fourth embodiment) areapplied. In these drawings, elements having same configurations andfunctions as those of the third embodiment are designated by samenumerals.

In this embodiment, an opening or hole 162 to which a shutter 160 isattached is formed in a sidewall of a chamber 10 at a height in themiddle of upper and lower electrodes 24 and 16, and a rod-shaped opticaltransmission probe 164 provided with a light receiving surface 164 c ata front end portion thereof is configured to be put into and drawn fromthe hole 162 in the radial direction of the chamber. The probe 164 maybe an optical fiber having a dual structure including a core 164 aformed of, e.g., quartz (synthetic quartz or fused quartz) or sapphire,and a cladding 164 b (FIG. 43).

The probe 164 is accommodated in a bellows 166 placed to freely expandand contract in the radial direction of the chamber outside the chamber10. A base portion of the probe 164 is horizontally supported by aslider 76 of an actuator 56, and is optically connected to a bundlefiber 134 through a connector 158. The bellows 166 is in contact withthe chamber 10 at one end thereof and the slider 76 at the other endthereof, which forms an airtight space around the probe 164. An insidespace of the bellows 166 is adapted to be depressurized to a vacuumdegree equal to that of the chamber 10 by a gas exhaust unit 170 througha gas exhaust pipe 168. A heater 172 (for example, a PTC element orresistant heating element) is provided inside or around the bellows 166to heat the probe 164 to a certain temperature (for example, atemperature around 100° C.).

In this embodiment, while plasma light emission measurement is not beingperformed, the shutter 160 is closed and the probe 164 is pulled out ofthe chamber 10, as shown in FIG. 41. However, before plasma lightemission measurement is performed, the inner space of the bellows 166 isdepressurized to a vacuum degree almost equal to that of the chamber 10,and the probe 164 is heated to a certain temperature. When plasma lightemission measurement is performed, the shutter 160 is opened, the linearactuator 56 is operated, to move rectilinearly the probe 164 in theaxial direction and inserted into the chamber 10 through the hole 162,as shown in FIG. 42. At this time, the bellows 166 contracts as theslider 76 and the probe 164 moves forward.

Light is incident on the light receiving surface 164 c of the probe 164from the plasma PZ in the chamber 10. The viewing angle of the probe 164is restricted by a numerical aperture NA that is determined by therefractive indices of the core 164 a and the cladding 164 b. A lightdistribution on a scan line can be measured by obtaining a variation ΔIof the luminous intensity of the plasma with respect to a minute movingdistance Δx using the measurement unit 132 while moving (scanning) theprobe 164 in the axial direction, i.e., the radial direction x of thechamber. Such a measurement scanning may be performed during any offorward (advance) and backward (return) movement of the probe 164.

Even through the cladding 164 b of the probe 164 is struck by the plasmaPZ in the chamber 10, the core 164 a propagating collected plasma lightis not influenced. Further, since the probe 164 has been heated to hightemperature outside the chamber 10, an amount of deposits are attachedthereto is small even though the probe 164 is exposed to the plasma PZin the chamber 10.

Since the probe 164 is made of non-metal, the probe 164 does not disturbthe plasma PZ and can perform scanning within a very short time (forexample, several seconds) compared to processing time (for example,several minutes), thus scarcely influencing processing results. For thisreason, it is possible to perform such a measurement scanning aplurality of times during processing time at regular intervals. Further,measurement results having high correlation with processing results canbe obtained. This embodiment may be applied to actual processing as wellas the development of processing. For example, this embodiment may beapplied to light emission monitoring used to control a process such asthe detection of a termination point in plasma etching.

In the above-described third and fourth embodiments, plasma lightemission is measured in the form of a spatial distribution while movingthe probes 130 and 164 in the axial direction of the chamber 10.However, in the present invention, it is possible to move the probe inthe chamber 10 in an arbitrary direction. For example, as shown in FIG.44, a plasma light distribution in the vertical direction z can bemeasured by obtaining a variation ΔI of the luminous intensity of theplasma with respect to a minute moving distance Δz using the measurementunit 132 while moving (scanning) the probe 130 in the vertical directionz in a plasma space in the chamber 10.

In the plasma light emission measuring apparatus of the presentinvention, some other plasma attribute can be obtained from the measuredvalues of the light emission of plasma obtained by the spectroscopicanalysis method described above. In general, emission species, such asan atom, a molecule, a radical and an ion, emit light at a uniquewavelength or spectrum corresponding to the internal energy statethereof. The luminous intensity I_(x) of a certain emission species isgiven by Equation 5.I _(x) =C _(x,λ) ·N _(x) n _(e)·∫σ_(x)(E)·v _(e) ·f _(e)(E)·dE  Eq. (5)where C_(x,λ) is a physical property value of the emission species (suchas wavelength, spontaneous emission probability, etc.) or a coefficientrepresenting a geometrical element related to a measurement system.Further, N_(x) is density of the emission species at a base energystate, n_(e) is electron density, σ_(x)(E) is the electroncollision-excited section of the emission species X, v_(e) is the speedof an electron, and f_(e)(E) is an electron energy distribution function(EEDF). Furthermore, the integration ∫ of Equation 5 ranges from 0 toinfinity (∞).

As described above, the light emission of plasma is determined byseveral plasma quantities. In other words, various quantities, such asthe density of an emission species, electron density and an electrondensity distribution, are obtained from the measured values of plasmalight emission.

For example, when N_(x) is obtained by using an actinometry method andelectron density N_(e) is obtained by using an electron densitymeasuring method, such as a PAP method or Langmuir probe method, anelectron energy distribution f_(e)(E) can be obtained from Equation 5.

In the plasma light emission measuring apparatus of the presentembodiment, it is possible to displace each element with a substitutehaving same function. For example, although, in the above embodiment,the quartz pipe 50 is installed to traverse the chamber 10 in the radialdirection like a bridge, it is possible to secure the quartz pipe 50 ata single location in a cantilever manner. Further, in this embodiment,the probes 130 and 164 are made to be moved in the axial direction, thatis, the radial direction of the chamber 10, by the rectilinear operationof the linear actuator 56. However, the probes 130 and 164 may be movedforward and backward in the axial direction of the quartz pipe 50 orchamber 10, or may be rectilinearly moved as in the above-describedembodiment in a manual manner.

FIGS. 45 to 47 show variants of this embodiment. A variant of FIG. 45 isformed by constructing the probe 130 of the first embodiment with abundle type optical guide including a plurality of optical fibers 166instead of a single body quartz rod. To integrate the plurality ofoptical fibers 166 into a single part, a heat-resistance non-metallicmember 168 is provided around the bundle. The material of theheat-resistant non-metallic member 168 is preferably a heat-resistantpolymer, e.g., polyimide, which may be wound around the bundle in theform of a tape or gathered in the form of a resin. Since such a bundletype probe 130 has an advantage in that it has such flexibility as notto be easily damaged.

A variant of FIG. 46 is formed by integrating such a bundle type probe130 to be inserted to the chamber 10 and a standard bundle fiber 134 tobe extended from the chamber 10. That is, each optical fiber 166 of theprobe 130 and each optical fiber 166 of the bundle fiber 134 form asingle continuous optical fiber, and the probe 130 and the bundle fiber134 are different in that a covering of the former 130 is an insulatingmaterial and a covering of the latter 134 is a metal. In accordance withthe integrated optical fiber, there is no couple loss between the probe130 and the bundle fiber 134, and the amount of light received by themeasurement unit 132 side [in particular, spectroscope 150] isincreased, thereby measurement precision being improved.

A variant of FIG. 47 is formed by constructing the mirror 140 of theprobe 130 with aluminum. Aluminum is a material having a certain highreflection factor for rays ranging from an ultraviolet ray to aninfrared ray, and can be used to be suitable for the mirror 140.However, aluminum is easily oxidized and then deteriorated. Accordingly,in this embodiment, aluminum is deposited on a side of the transparentquartz substrate 170, and an aluminum-deposited film 172 and thetransparent quartz substrate 170 are attached to a cylindrical body 138made of SUS, with the aluminum-deposited film 172 functioning as amirror protecting material being placed on the front side thereof andthe transparent quartz substrate 170 functioning as a reflective filmbeing placed on the back side thereof. The light of plasma PL to bemeasured is transmitted through the transparent quartz substrate 170 andreflected by the aluminum-deposited film 172. In another variant,although not shown, a cylindrical body 138 may be made of aluminum and areflective surface or mirror surface 140 may be coated with a protectivefilm made of magnesium fluoride.

An application of the plasma light emission measuring apparatus of thepresent invention is to monitor abnormal discharge in a chamber. Forexample, in the embodiment of FIG. 32, when the gas discharge hole(exhaust hole) 26 of the upper electrode 24 having a shower headstructure is widened due to abrasion to cause abnormal discharge, thesituation of abnormal discharge can be observed if the probe 130 is madeto scan in the horizontal direction with the light collecting unit 144of the probe 130 being directed upward. FIG. 48 shows an example of theapplication. As shown in the drawing, there is formed a spatialdistribution having a pattern in which, when the gas discharge hole 26of the upper electrode 24 has an abnormality (widened), light emissionfrom the central portion of the electrode is decreased while the lightemission from the outer portion thereof is increased, compared to alight emission distribution formed in the case where the gas dischargehole 26 of the upper electrode 24 is in a normal state. From this, it ispossible to detect the occurrence of abnormal discharge and locationsthereof. The experimental data of FIG. 48 is obtained by monitoring Arradical light emission in silicon dioxide film etching. Basic plasmacreating conditions (recipe) were as follows:

wafer diameter: 300 mm

gas pressure: 25 mTorr

distance between upper and lower electrodes: 35 mm

etching gas: C₅F₈/O₂/Ar=29/750/47 sccm

RF power: upper/lower=3300/3800 W

wafer backside pressure(center portion/edge portion): 10/40 Torr

The above-described abnormal discharge monitoring function can berealized by the plasma electron density measuring methods andapparatuses in accordance with the first embodiment (FIG. 1) or thesecond embodiment (FIG. 19). FIG. 49 shows experimental data obtained bythe plasma resonance probe method of the first embodiment (FIG. 1). Thestructure of a chamber and plasma creation conditions are same as thoseshown in FIG. 48. As shown in FIG. 49, there is formed a spatialdistribution having a pattern in which, when the gas discharge hole 26of the upper electrode 24 has an abnormality (widened), light emissionfrom the central and outer portions of the electrode is increased,compared to a light emission distribution formed in the case where thegas discharge hole 26 of the upper electrode 24 is normal. From this, itis possible to detect the occurrence of abnormal discharge and locationsthereof.

Various modifications can be made in the plasma processing apparatus ofthe present invention. In particular, the capacitively coupled parallelflat plate plasma creation method is an example, and the presentinvention can be applied to other methods, such as a magnetron methodand an Electron Cyclotron Resonance (ECR) method. Further, the type ofplasma processing is not limited to etching, but the present inventioncan be applied to some other plasma processing, such as chemical vapordeposition (CVD), oxidation or sputtering. Further, an object to beprocessed by the plasma processing is not limited to a semiconductorwafer, but the present invention can be applied to, for example, a glasssubstrate or liquid crystal display (LCD) substrate. The plasma lightemission measuring method and apparatus of the present invention can beapplied to plasma apparatuses other than the plasma processingapparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

[FIG. 1] shows a configuration of a plasma processing apparatus to whichplasma electron density measuring method and apparatus are applied inaccordance with a first embodiment of the present invention;

[FIG. 2] is a partially enlarged view showing principal parts of a probeof an embodiment;

[FIG. 3] illustrates a block diagram showing a configuration ofprincipal parts of a vector network analyzer and a measurement controlunit in the measuring unit of the embodiment;

[FIG. 4] schematically describes a state of a first batch measurementprocess in an embodiment;

[FIG. 5] schematically depicts a state of a second batch measurementprocess in an embodiment;

[FIG. 6] is a graph showing the frequency characteristics (experimentaldata) of the absolute values, real parts and imaginary parts of complexreflection coefficients obtained by using the plasma resonance probemethod of the present invention;

[FIG. 7A] exhibits an example (experimental data) of the measurementsensitivity of electron density obtained by using the plasma resonanceprobe method of the present invention;

[FIG. 7B] exhibits an example (experimental data) of the measurementsensitivity of electron density obtained by using the plasma resonanceprobe method of the present invention;

[FIG. 8] charts a measured value of electron density obtained inaccordance with the present invention together with that of electrondensity obtained by using a PAP method;

[FIG. 9] is a graph showing the frequency characteristics (experimentaldata) of complex reflection coefficients obtained under a relativelylow-pressure condition (15 mTorr);

[FIG. 10] is a graph showing the frequency characteristics (experimentaldata) of complex reflection coefficients obtained under a high pressurecondition (800 mTorr);

[FIG. 11] is a graph showing the frequency characteristics (experimentaldata) of complex reflection coefficients obtained under a high pressurecondition (1600 mTorr);

[FIG. 12] is a graph showing the frequency characteristics (experimentaldata) of complex reflection coefficients obtained under a high pressurecondition (2000 mTorr);

[FIG. 13] illustrates a configuration of a plasma processing apparatusto which a plasma electron density measuring apparatus is applied inaccordance with another embodiment of the present invention;

[FIG. 14A] describes a sectional view showing an example of probe unitthat can be used in the embodiment of FIG. 13;

[FIG. 14B] describes a sectional view showing an example of probe unitthat can be used in the embodiment of FIG. 13;

[FIG. 15] is a perspective view showing examples of probe portions thatcan be used in the embodiment of FIG. 13;

[FIG. 16] provides a configuration of a plasma processing apparatus towhich a plasma electron density measuring apparatus is applied inaccordance with still another embodiment of the present invention;

[FIG. 17] is a graph showing an example of a situation in which anetching rate is gradually decreased and stabilized at respectivelocations on a wafer in the etching cycle of seasoning;

[FIG. 18] depicts time variations of the average value of etching ratesand electron density;

[FIG. 19] charts a configuration of a plasma processing apparatus towhich plasma monitoring method and apparatus are applied in accordancewith a second embodiment of the present invention;

[FIG. 20] is a flowchart showing a schematic sequence of plasmamonitoring process in an embodiment;

[FIG. 21] is a flowchart showing a detailed sequence of a first batchmeasurement process in the plasma monitoring process of the secondembodiment;

[FIG. 22] is a flowchart showing a detailed sequence of a second batchmeasurement process in the plasma monitoring process of the secondembodiment;

[FIG. 23] is a graph showing an example of the spatial distributioncharacteristics of electron density obtained in the second embodimentwhile comparing the example with a comparative example;

[FIG. 24] charts a graph showing the frequency characteristics of noisepeaks in an embodiment;

[FIG. 25] exhibits a graph showing the actually measured values andcalculated values of standing wave noise depending the insertion lengthof a probe;

[FIG. 26A] shows a graph of frequency characteristics that represent thenoise absorption effect of an electromagnetic wave absorber in anembodiment;

[FIG. 26B] shows a graph of frequency characteristics that represent thenoise absorption effect of an electromagnetic wave absorber in anembodiment;

[FIG. 27] is a graph showing frequency characteristics that representthe noise absorption effect of an electromagnetic wave absorber in anembodiment;

[FIG. 28] illustrates a graph of frequency characteristics thatrepresent a signal increase effect according to the enhancement of anelectromagnetic wave absorber in an embodiment;

[FIG. 29] charts a graph showing the spatial distributioncharacteristics of electron density in an embodiment;

[FIG. 30] charts a graph showing the spatial distributioncharacteristics of electron density in an embodiment;

[FIG. 31] charts a graph showing the spatial distributioncharacteristics of electron density in an embodiment;

[FIG. 32] provides a configuration of a plasma processing apparatus towhich plasma light emission measuring method and apparatus are appliedin accordance with a third embodiment of the present invention;

[FIG. 33] exhibits a partially enlarged section showing constructionsand operations of principal parts of a probe in the third embodiment;

[FIG. 34A] shows a partially enlarged section showing a structure of aprobe in another embodiment;

[FIG. 34B] shows a partially enlarged section showing a structure of aprobe in another embodiment;

[FIG. 35] is a diagram schematically showing an operation of a probe anda bundle fiber in the third embodiment;

[FIG. 36] is a partially enlarged section showing a construction andoperation of a probe in an embodiment;

[FIG. 37] charts a graph of a relationship between refractive indexesand cut angles of a quartz rod used in the probe in the thirdembodiment;

[FIG. 38A] charts a graph showing an example of a correlation betweenthe intra-surface distribution of etching rates and the spatialdistribution of plasma light emission in the third embodiment;

[FIG. 38B] charts a graph showing an example of a correlation betweenthe intra-surface distribution of etching rates and the spatialdistribution of plasma light emission in the third embodiment;

[FIG. 39A] charts a graph showing an example of a correlation betweenthe intra-surface distribution of etching rates and the spatialdistribution of plasma light emission in the third embodiment;

[FIG. 39B] charts a graph showing an example of a correlation betweenthe intra-surface distribution of etching rates and the spatialdistribution of plasma light emission in the third embodiment;

[FIG. 40A] charts a graph showing an example of a correlation betweenthe intra-surface distribution of etching rates and the spatialdistribution of plasma light emission in the third embodiment;

[FIG. 40B] charts a graph showing an example of a correlation betweenthe intra-surface distribution of etching rates and the spatialdistribution of plasma light emission in the third embodiment;

[FIG. 41] describes a configuration of a plasma processing apparatus towhich plasma light emission measuring method and apparatus are appliedin accordance with another embodiment of the present invention;

[FIG. 42] shows a state of plasma spectroscopic measurement in theplasma processing apparatus of FIG. 41;

[FIG. 43] is a diagram showing an operation of the plasma light emissionmeasuring apparatus of FIG. 41;

[FIG. 44] is a diagram showing a plasma light emission measuring methodin accordance with another embodiment;

[FIG. 45] is a diagram showing a configuration of principal parts of anoptical transmission probe in accordance with a variant;

[FIG. 46] is a diagram showing a configuration of principal parts of anoptical transmission probe in accordance with a variant;

[FIG. 47] is a diagram showing a configuration of principal parts of anoptical transmission probe in accordance with a variant;

[FIG. 48] is a graph showing the experimental results of a function ofmonitoring an abnormal discharge in a chamber in accordance with theplasma light emission measuring method of the present invention;

[FIG. 49] is a graph showing the experimental results of a function ofmonitoring an abnormal discharge in a chamber in accordance with theplasma resonance probe method of the present invention; and

[FIG. 50] illustrates a diagram for explaining a conventional PAPmethod.

DESCRIPTION OF REFERENCE NUMERALS

10: chamber

10 a: through hole (support)

16: susceptor (lower electrode)

18, 38: high-frequency power supply

20: main control unit

24: upper electrode

34: processing gas supply unit

50: insulating pipe

52: coaxial cable

52 a: probe portion (antenna probe)

54: measuring unit

56: linear actuator

58: O-ring

62: grounding conductor

66: electromagnetic wave absorber

68: vector network analyzer

74: measurement control unit

80: cooling gas supply unit

82: gas pipe

84: reflection coefficient measuring unit

90: imaginary part memory

92: resonance frequency determining unit

94: electron density operation unit

100, 102, 104: probe unit

108: window member

114: selection switch

120: scalar network analyzer

122: measurement control unit

130: optical transmission probe

132: measurement unit

134: bundle fiber

136: cap

140: mirror

142: window

144: light collecting unit

146: cladding

148: black paint

150: spectroscope

152: photoelectric conversion unit

154: measurement operation unit

160: shutter

162: hole

164: optical transmission probe

166: bellows

170: exhaust unit

172: heater

1. A method of monitoring plasma, comprising the steps of: placing an antenna probe at a monitoring location set inside or near plasma existing within a certain space; causing the antenna probe to irradiate a frequency-variable electromagnetic wave into the plasma; receiving an electromagnetic wave reflected from the plasma to the antenna probe; measuring a complex reflection coefficient based on the incident and reflected electromagnetic waves, and obtaining an imaginary part of the complex reflection coefficient; measuring a resonance frequency at which the imaginary part of the complex reflection coefficient is zero by sweeping the frequencies of the electromagnetic wave; and calculating electron density in the plasma based on the measured resonance frequency.
 2. The method of claim 1, where a frequency at a point where a sign of the imaginary part of the complex reflection coefficient changes is determined as the resonance frequency by sweeping the frequencies of the electromagnetic waves.
 3. The method of claim 2, further comprising the steps of: in a state where the plasma does not exist in the space, obtaining a first frequency characteristic with respect to the imaginary part of the complex reflection coefficient by sweeping the frequencies of the electromagnetic waves; in a state where the plasma exists in the space, obtaining a second frequency characteristic with respect to the imaginary part of the complex reflection coefficient by sweeping the frequencies of the electromagnetic waves; and obtaining a normalized frequency characteristic based on the first and second frequency characteristics.
 4. The method of claim 1, wherein an insulating pipe is placed in or in the vicinity of the plasma between first and second supports provided in sidewalls of the chamber in which the plasma is created; and a probe portion is positioned at the monitoring location in such a way as to insert a coaxial cable, which is the antenna probe and has the probe portion with a front core wire thereof being exposed, from one end of the insulating pipe.
 5. The method of claim 4, wherein the coaxial cable is moved in the axial direction of the insulating pipe to change the monitoring location.
 6. The method of claim 5, wherein the spatial distribution of electron density in the plasma is obtained after the location of the probe portion within the insulating pipe is changed.
 7. An apparatus for monitoring plasma, comprising: an antenna probe located in a wall of or inside a chamber in or into which plasma is created or introduced; a vector reflection coefficient measuring unit for, while sweeping frequencies, transmitting electromagnetic waves of respective frequencies to the antenna probe to be irradiated to the plasma, receiving reflected waves from the plasma through the antenna probe, and measuring complex reflection coefficients; a resonance frequency measuring unit for measuring a resonance frequency at which an imaginary part of the complex reflection coefficients is zero; and an electron density operation unit for calculating electron density in the plasma based on the measured resonance frequency.
 8. The apparatus of claim 7, wherein the reflection coefficient measuring unit obtains frequency characteristic with respect to the imaginary part of the complex reflection coefficient by sweeping the frequencies of the electromagnetic waves; and the resonance frequency measuring unit determines as the resonance frequency a frequency at a point where a sign of the imaginary part of the complex reflection coefficient changes in the frequency characteristics.
 9. The apparatus of claim 8, wherein the reflection coefficient measuring unit obtains a first frequency characteristic in a state where the plasma does not exist in the chamber, a second frequency characteristic in a state where the plasma exists in the chamber, and a normalized frequency characteristic based on the first and second frequency characteristics, with respect to the imaginary part of the complex reflection coefficient.
 10. The apparatus of claim 9, further comprising: an insulating pipe inserted into and installed in the chamber; and a coaxial cable used as the antenna probe, provided with a probe portion formed by exposing a front core wire of the coaxial cable, and inserted into the insulating pipe from one end of the insulating pipe.
 11. The apparatus of claim 9, further comprising an actuator for moving the coaxial cable in the axial direction of the insulating pipe.
 12. The apparatus of claim 10, wherein the insulating pipe is hung between first and second supports provided in the sidewalls of the chamber.
 13. The apparatus of claim 12, wherein at least one of the first and second supports is formed of a through hole.
 14. The apparatus of claim 13, further comprising an O-ring for air-tightly and fixedly attaching the insulating pipe in the through hole.
 15. The apparatus of claim 10, further comprising a grounding conductor one end of which is connected to a grounding potential portion of the chamber and the other end of which is connected to the outer conductor of the coaxial cable.
 16. The apparatus of claim 15, wherein an electromagnetic wave absorber for absorbing a noise signal propagating along the outer conductor through electromagnetic induction is provided at a location of the probe portion side of the coaxial cable when viewed from a location where the grounding conductor and the outer conductor of the coaxial cable are in contact with each other.
 17. The apparatus of claim 16, wherein the electromagnetic wave absorber includes one or more bead-shaped ferrite members placed around the coaxial cable along the axial direction thereof.
 18. The apparatus of claim 10, further comprising a cooling mechanism connected to the other end of the insulating pipe to allow cooling gas to flow inside the insulating pipe.
 19. A plasma processing apparatus, comprising: a chamber for accommodating therein an object to be processed; a gas supply unit for supplying certain gas into the chamber; a plasma creation unit for creating plasma, which is used to perform treatment on the object to be processed, by discharging electricity in the gas in the chamber; a gas exhaust unit for maintaining the chamber at certain pressure by depressurizing the inside of the chamber; an antenna probe located in the wall of or inside the chamber in or into which the plasma is created or introduced; and a plasma monitoring device including: a vector reflection coefficient measuring unit for, while sweeping frequencies, transmitting electromagnetic waves of respective frequencies to the antenna probe to be irradiated to the plasma, receiving reflected waves from the plasma through the antenna probe, and measuring complex reflection coefficients; a resonance frequency measuring unit for measuring a resonance frequency at which an imaginary part of the complex reflection coefficients is zero; and an electron density operation unit for calculating electron density in the plasma based on the measured resonance frequency.
 20. The apparatus of claim 19, further comprising a monitor unit for monitoring a state of plasma processing in the chamber based on the electron density obtained by the plasma monitoring apparatus.
 21. The apparatus of claim 19, further comprising a process control unit for controlling at least one of process parameters influencing plasma processing, thereby maintaining the electron density obtained by the plasma monitoring apparatus to be within a certain range.
 22. The apparatus of claim 19, further comprising a seasoning control unit for performing seasoning based on the characteristic of the time variation of the electron density obtained by the plasma monitoring apparatus with respect to processing conditions after the cleaning of the chamber or the replacement of parts.
 23. The apparatus of claim 22, wherein the seasoning control unit obtains a representative of the measured electron densities time-varying during the plasma processing with respect to respective dummy substrates being plasma-processed in the chamber, completing the seasoning when the representative is stabilized to an actual normal value between successive dummy substrates, and changes the dummy substrate being put into the chamber from to a normal substrate to be processed.
 24. The apparatus of claim 19, wherein the antenna probe is attached to the wall of the chamber.
 25. The apparatus of claim 19, wherein electrodes for creating the plasma are provided in the chamber, and the antenna probe is attached to the electrodes.
 26. The apparatus of claim 19, wherein a mounting table for mounting the object to be processed is provided in the chamber, and the antenna probe is attached to the mounting table.
 27. The apparatus of claim 19, further comprising a selection switch for selecting any one of a plurality of antenna probes arranged at different locations to be electrically connected to the reflection coefficient measuring unit.
 28. The apparatus of claim 27, wherein the selection switch electrically connects the plurality of antenna probes to the reflection coefficient measuring unit sequentially in a time division manner.
 29. A method of monitoring plasma, comprising the steps of: placing an antenna probe at a monitoring location set inside or in the vicinity of plasma existing within a certain space; irradiating a frequency-variable electromagnetic waves from the antenna probe to the plasma; receiving an electromagnetic waves reflected from the plasma to the antenna probe; measuring a phase difference between the incident and reflected waves; measuring a resonance frequency at which the phase difference is zero while sweeping the frequencies of the electromagnetic waves; and calculating electron density in the plasma based on the measured resonance frequency.
 30. An apparatus for monitoring plasma, comprising: an antenna probe located in the wall of or inside a chamber in or into which plasma is created or introduced; a phase difference measuring unit for, while sweeping frequencies, transmitting electromagnetic waves of respective frequencies to the antenna probe to be irradiated to the plasma, receiving reflected waves from the plasma through the antenna probe, and measuring a phase difference between the incident and reflected waves; a resonance frequency measuring unit for measuring a resonance frequency at which the phase difference obtained by the phase difference measuring unit is zero; and an electron density operation unit for calculating electron density in the plasma based on the measured resonance frequency.
 31. A plasma processing apparatus, comprising: a chamber for accommodating therein an object to be processed; a gas supply unit for supplying certain gas into the chamber; a plasma creation unit for creating plasma, which is used to perform treatment on the object to be processed, by discharging electricity in the gas in the chamber; a gas exhaust unit for maintaining the chamber at a certain pressure by depressurizing the inside of the chamber; an antenna probe located in the wall of or inside the chamber in or into which the plasma is created or introduced; and a plasma monitoring device including: a phase difference measuring unit for, while sweeping frequencies, transmitting an electromagnetic wave of respective frequencies to the antenna probe to be irradiated to the plasma, receiving reflected waves from the plasma through the antenna probe, and measuring a phase difference between the incident and reflected waves; a resonance frequency measuring unit for measuring a resonance frequency at which the phase difference obtained by the phase difference measuring unit is zero; and an electron density operation unit for calculating electron density in the plasma based on the measured resonance frequency. 